diff --git a/include/xlnt/cell/cell.hpp b/include/xlnt/cell/cell.hpp
index 82ddf70d..f81e9081 100644
--- a/include/xlnt/cell/cell.hpp
+++ b/include/xlnt/cell/cell.hpp
@@ -32,6 +32,8 @@
 
 namespace xlnt {
     
+enum class calendar;
+    
 class cell_reference;
 class comment;
 class relationship;
@@ -107,28 +109,22 @@ public:
     bool has_hyperlink() const;
     
     // style
-    bool has_style() const;
-    style &get_style();
-    const style &get_style() const;
-    void set_style(const style &s);
-    
-    // style shortcuts
-    std::string get_number_format();
-    std::string get_number_format() const;
-    void set_number_format(const std::string &format_code, int index = -1);
-    font &get_font();
+    std::size_t get_style_id() const;
+    const number_format &get_number_format() const;
+    void set_number_format(const number_format &format);
     const font &get_font() const;
-    fill &get_fill();
+    void set_font(const font &font_);
     const fill &get_fill() const;
-    border &get_border();
+    void set_fill(const fill &fill_);
     const border &get_border() const;
-    alignment &get_alignment();
+    void set_border(const border &border_);
     const alignment &get_alignment() const;
-    protection &get_protection();
+    void set_alignment(const alignment &alignment_);
     const protection &get_protection() const;
-    bool pivot_button();
+    void set_protection(const protection &protection_);
+    void set_pivot_button(bool b);
     bool pivot_button() const;
-    bool quote_prefix();
+    void set_quote_prefix(bool b);
     bool quote_prefix() const;
     
     // comment
@@ -168,6 +164,8 @@ public:
     worksheet get_parent();
     const worksheet get_parent() const;
     
+    calendar get_base_date() const;
+    
     // operators
     cell &operator=(const cell &rhs);
     
@@ -178,8 +176,10 @@ public:
     friend bool operator<(cell left, cell right);
     
 private:
-    void set_value_guess_type(const std::string &s);
     friend class worksheet;
+    friend struct detail::cell_impl;
+    friend class style;
+    
     cell(detail::cell_impl *d);
     detail::cell_impl *d_;
 };
diff --git a/include/xlnt/common/datetime.hpp b/include/xlnt/common/datetime.hpp
index c0296f8f..6918ce8a 100644
--- a/include/xlnt/common/datetime.hpp
+++ b/include/xlnt/common/datetime.hpp
@@ -152,6 +152,8 @@ struct datetime
 /// </summary>
 struct timedelta
 {
+    static timedelta from_number(long double number);
+    
     timedelta(int days_, int hours_, int minutes_ = 0, int seconds_ = 0, int microseconds_ = 0)
     : days(days_),
       hours(hours_),
diff --git a/include/xlnt/reader/workbook_reader.hpp b/include/xlnt/reader/workbook_reader.hpp
index 2cfb162c..cbe96032 100644
--- a/include/xlnt/reader/workbook_reader.hpp
+++ b/include/xlnt/reader/workbook_reader.hpp
@@ -31,5 +31,6 @@ namespace xlnt {
 class workbook;
 
 xlnt::workbook load_workbook(const std::vector<std::uint8_t> &bytes);
+xlnt::workbook load_workbook(const std::string &filename);
 
 } // namespace xlnt
diff --git a/include/xlnt/styles/alignment.hpp b/include/xlnt/styles/alignment.hpp
index 161d0063..7dd5e64b 100644
--- a/include/xlnt/styles/alignment.hpp
+++ b/include/xlnt/styles/alignment.hpp
@@ -64,6 +64,8 @@ public:
         && indent_ == other.indent_;
     }
     
+    std::size_t hash() const { return 0; }
+    
 private:
     horizontal_alignment horizontal_ = horizontal_alignment::general;
     vertical_alignment vertical_ = vertical_alignment::bottom;
diff --git a/include/xlnt/styles/borders.hpp b/include/xlnt/styles/borders.hpp
index 5f5692e5..a65f3055 100644
--- a/include/xlnt/styles/borders.hpp
+++ b/include/xlnt/styles/borders.hpp
@@ -23,6 +23,8 @@
 // @author: see AUTHORS file
 #pragma once
 
+#include <cstddef>
+
 #include <xlnt/styles/color.hpp>
 
 namespace xlnt {
@@ -103,6 +105,8 @@ public:
         && diagonal_up == other.diagonal_up
         && diagonal_down == other.diagonal_down;
     }
+    
+    std::size_t hash() const { return 0; }
 };
 
 } // namespace xlnt
diff --git a/include/xlnt/styles/fill.hpp b/include/xlnt/styles/fill.hpp
index 9ff28c67..12dc4234 100644
--- a/include/xlnt/styles/fill.hpp
+++ b/include/xlnt/styles/fill.hpp
@@ -60,10 +60,12 @@ public:
     color start_color = color::white;
     color end_color = color::black;
     
-    bool operator==(const fill &other) const
+    virtual bool operator==(const fill &other) const
     {
         return type_ == other.type_;
     }
+    
+    virtual std::size_t hash() const { return 0; }
 };
 
 class pattern_fill : public fill
@@ -72,6 +74,8 @@ public:
     void set_pattern_type(const std::string &type) { type_ = type; }
     void set_foreground_color(const std::string &hex) { foreground_color_ = hex; }
     
+    std::size_t hash() const override { return 0; }
+    
 private:
     std::string type_;
     std::string foreground_color_;
diff --git a/include/xlnt/styles/font.hpp b/include/xlnt/styles/font.hpp
index b0a49329..41b57626 100644
--- a/include/xlnt/styles/font.hpp
+++ b/include/xlnt/styles/font.hpp
@@ -28,6 +28,8 @@
 #include <xlnt/styles/color.hpp>
 
 namespace xlnt {
+    
+class style;
 
 class font
 {
@@ -56,7 +58,15 @@ public:
         && color_ == other.color_;
     }
     
+    int get_size() const { return size_; }
+    std::string get_name() const { return name_; }
+    bool is_bold() const { return bole_; }
+    
+    std::size_t hash() const { return 0; }
+    
 private:
+    friend class style;
+    
      std::string name_ = "Calibri";
      int size_ = 11;
      bool bold_ = false;
diff --git a/include/xlnt/styles/number_format.hpp b/include/xlnt/styles/number_format.hpp
index dde0e70c..9f8658d0 100644
--- a/include/xlnt/styles/number_format.hpp
+++ b/include/xlnt/styles/number_format.hpp
@@ -86,55 +86,27 @@ public:
     static std::string builtin_format_code(int index);
     static format lookup_format(int code);
     
-    static bool is_date_format(const std::string &format);
     static bool is_builtin(const std::string &format);
     
-    number_format() : format_code_(format::general), format_index_(0) {}
-    number_format(format code) : format_code_(code), format_index_(reversed_builtin_formats().at(format_strings().at(code))) {}
+    number_format();
+    number_format(format code);
+    number_format(const std::string &code);
     
-    format get_format_code() const { return format_code_; }
+    format get_format_code() const;
     
-    void set_format_code(format format_code, int index = -1)
-    {
-        format_code_ = format_code;
-        
-        if(format_code_ != format::unknown)
-        {
-            set_format_code_string(format_strings().at(format_code), index);
-        }
-    }
+    void set_format_code(format format_code);
     
-    void set_format_code_string(const std::string &format_code, int index)
-    {
-        custom_format_code_ = format_code;
-        format_index_ = index;
-        
-        const auto &reversed = reversed_builtin_formats();
-        auto match = reversed.find(format_code);
-        
-        format_code_ = format::unknown;
-        
-        if(match != reversed.end())
-        {
-            format_index_ = match->second;
-            
-            for(const auto &p : format_strings())
-            {
-                if(p.second == format_code)
-                {
-                    format_code_ = p.first;
-                    break;
-                }
-            }
-        }
-        
-    }
-    std::string get_format_code_string() const;
+    void set_format_string(const std::string &format_code);
+    std::string get_format_string() const;
+    
+    int get_format_index() const { return format_index_; }
+    
+    std::size_t hash() const;
 
 private:
-    std::string custom_format_code_ = "";
-    format format_code_ = format::general;
-    int format_index_ = 0;
+    format format_code_;
+    int format_index_;
+    std::string format_string_;
 };
 
 } // namespace xlnt
diff --git a/include/xlnt/styles/protection.hpp b/include/xlnt/styles/protection.hpp
index ed15482c..e8f23bf7 100644
--- a/include/xlnt/styles/protection.hpp
+++ b/include/xlnt/styles/protection.hpp
@@ -23,6 +23,8 @@
 // @author: see AUTHORS file
 #pragma once
 
+#include <cstddef>
+
 namespace xlnt {
 
 class protection
@@ -48,6 +50,8 @@ public:
         return locked_ == other.locked_ && hidden_ == other.hidden_;
     }
     
+    std::size_t hash() const { return 0; }
+    
 private:
     type locked_;
     type hidden_;
diff --git a/include/xlnt/styles/style.hpp b/include/xlnt/styles/style.hpp
index 4d079898..1df36535 100644
--- a/include/xlnt/styles/style.hpp
+++ b/include/xlnt/styles/style.hpp
@@ -23,64 +23,55 @@
 // @author: see AUTHORS file
 #pragma once
 
-#include "font.hpp"
-#include "fill.hpp"
-#include "borders.hpp"
-#include "alignment.hpp"
-#include "color.hpp"
-#include "number_format.hpp"
-#include "protection.hpp"
-
 namespace xlnt {
+namespace detail {
+    
+struct cell_impl;
+    
+} // namespace detail    
+
+class alignment;
+class border;
+class font;
+class fill;
+class number_format;
+class protection;
+    
+class cell;
 
 class style
 {
 public:
-    style(bool is_static = false) : static_(is_static) {}
+    const style default_style();
+    
+    style();
     style(const style &rhs);
+    style &operator=(const style &rhs);
     
     style copy() const;
     
-    font &get_font();
+    std::size_t hash() const;
+    
     const font &get_font() const;
-    void set_font(font font);
-    
-    fill &get_fill();
     const fill &get_fill() const;
-    void set_fill(fill &fill);
-    
-    border &get_border();
     const border &get_border() const;
-    void set_border(border borders);
-    
-    alignment &get_alignment();
-    const alignment get_alignment() const;
-    void set_alignment(alignment alignment);
-    
-    number_format &get_number_format() { return number_format_; }
-    const number_format &get_number_format() const { return number_format_; }
-    void set_number_format(number_format number_format);
-    
-    protection &get_protection();
+    const alignment &get_alignment() const;
+    const number_format &get_number_format() const;
     const protection &get_protection() const;
-    void set_protection(protection protection);
-    
-    bool pivot_button();
-    void set_pivot_button(bool pivot);
-    
-    bool quote_prefix();
-    void set_quote_prefix(bool quote);
+    bool pivot_button() const;
+    bool quote_prefix() const;
     
 private:
-    bool static_ = false;
-    font font_;
-    fill fill_;
-    border border_;
-    alignment alignment_;
-    number_format number_format_;
-    protection protection_;
-    bool pivot_button_;
-    bool quote_prefix_;
+    cell get_parent();
+    const cell get_parent() const;
+    detail::cell_impl *parent_;
+    std::size_t font_id_;
+    std::size_t fill_id_;
+    std::size_t border_id_;
+    std::size_t alignment_id_;
+    std::size_t number_format_id_;
+    std::size_t protection_id_;
+    std::size_t style_id_;
 };
 
 } // namespace xlnt
diff --git a/include/xlnt/workbook/workbook.hpp b/include/xlnt/workbook/workbook.hpp
index 08b278a0..75bde206 100644
--- a/include/xlnt/workbook/workbook.hpp
+++ b/include/xlnt/workbook/workbook.hpp
@@ -41,11 +41,13 @@ class drawing;
 class fill;
 class font;
 class named_range;
+class number_format;
 class pattern_fill;
 class protection;
 class range;
 class range_reference;
 class relationship;
+class style;
 class worksheet;
 class zip_file;
     
@@ -206,11 +208,36 @@ public:
     void add_color(color c);
     void add_number_format(const std::string &format);
     
+    const std::unordered_map<std::size_t, alignment> &get_alignments() const;
+    const std::unordered_map<std::size_t, border> &get_borders() const;
+    const std::unordered_map<std::size_t, fill> &get_fills() const;
+    const std::unordered_map<std::size_t, font> &get_fonts() const;
+    const std::unordered_map<std::size_t, number_format> &get_number_formats() const;
+    const std::unordered_map<std::size_t, protection> &get_protections() const;
+    
+    const number_format &get_number_format(std::size_t style_id) const;
+    std::size_t set_number_format(const number_format &format, std::size_t style_id);
+    const font &get_font(std::size_t style_id) const;
+    std::size_t set_font(const font &font_, std::size_t style_id);
+    const fill &get_fill(std::size_t style_id) const;
+    std::size_t set_fill(const fill &fill_, std::size_t style_id);
+    const border &get_border(std::size_t style_id) const;
+    std::size_t set_border(const border &border_, std::size_t style_id);
+    const alignment &get_alignment(std::size_t style_id) const;
+    std::size_t set_alignment(const alignment &alignment_, std::size_t style_id);
+    const protection &get_protection(std::size_t style_id) const;
+    std::size_t set_protection(const protection &protection_, std::size_t style_id);
+    bool get_pivot_button(std::size_t style_id) const;
+    bool get_quote_prefix(std::size_t style_id) const;
+    
     void set_code_name(const std::string &code_name);
     
     bool has_loaded_theme();
     std::string get_loaded_theme();
     
+    style get_style(std::size_t style_id);
+    std::size_t add_style(style style_);
+    
 private:
     friend class worksheet;
     std::shared_ptr<detail::workbook_impl> d_;
diff --git a/include/xlnt/writer/style_writer.hpp b/include/xlnt/writer/style_writer.hpp
index abd551b4..864f6f05 100644
--- a/include/xlnt/writer/style_writer.hpp
+++ b/include/xlnt/writer/style_writer.hpp
@@ -39,10 +39,8 @@ public:
     style_writer(workbook &wb);
     style_writer(const style_writer &);
     style_writer &operator=(const style_writer &);
-    std::unordered_map<std::size_t, std::string> get_style_by_hash() const;
-    std::string write_table() const;
-    std::vector<style> get_styles() const;
     
+    std::string write_table() const;
     std::string write_number_formats();
     
 private:
@@ -56,7 +54,6 @@ private:
     void write_dxfs();
     void write_table_styles();
     
-    std::vector<style> style_list_;
     workbook &wb_;
 };
     
diff --git a/source/cell.cpp b/source/cell.cpp
index fab54db1..b4deced4 100644
--- a/source/cell.cpp
+++ b/source/cell.cpp
@@ -6,12 +6,12 @@
 #include <xlnt/cell/cell_reference.hpp>
 #include <xlnt/cell/comment.hpp>
 #include <xlnt/common/datetime.hpp>
-#include <xlnt/common/relationship.hpp>
-#include <xlnt/worksheet/worksheet.hpp>
 #include <xlnt/common/exceptions.hpp>
+#include <xlnt/common/relationship.hpp>
 #include <xlnt/workbook/workbook.hpp>
 #include <xlnt/workbook/document_properties.hpp>
-#include <xlnt/common/exceptions.hpp>
+#include <xlnt/worksheet/worksheet.hpp>
+#include <xlnt/styles/color.hpp>
 
 #include "detail/cell_impl.hpp"
 #include "detail/comment_impl.hpp"
@@ -87,6 +87,36 @@ std::vector<std::string> split_string(const std::string &string, char delim)
     return split;
 }
 
+std::vector<std::string> split_string_any(const std::string &string, const std::string &delims)
+{
+    std::vector<std::string> split;
+    std::string::size_type previous_index = 0;
+    auto separator_index = string.find_first_of(delims);
+    
+    while(separator_index != std::string::npos)
+    {
+        auto part = string.substr(previous_index, separator_index - previous_index);
+        
+        if(!part.empty())
+        {
+            split.push_back(part);
+        }
+        
+        previous_index = separator_index + 1;
+        separator_index = string.find_first_of(delims, previous_index);
+    }
+    
+    split.push_back(string.substr(previous_index));
+    
+    return split;
+}
+
+bool is_date_format(const std::string &format_string)
+{
+    auto not_in = format_string.find_first_not_of("/-:, mMyYdDhHsS");
+    return not_in == std::string::npos;
+}
+
 bool is_valid_color(const std::string &color)
 {
     static const std::vector<std::string> colors = { "Black", "Green"
@@ -288,14 +318,180 @@ format_sections parse_format_sections(const std::string &combined)
     return result;
 }
 
-std::string format_section(long double number, const section &format)
+const std::vector<std::string> MonthNames =
 {
-    if(number == static_cast<long long int>(number))
+    "January",
+    "February",
+    "March",
+    "April",
+    "May",
+    "June",
+    "July",
+    "August",
+    "September",
+    "October",
+    "November",
+    "December"
+};
+
+std::string format_section(long double number, const section &format, xlnt::calendar base_date)
+{
+    const std::string unquoted = "$+(:^'{<=-/)!&~}> ";
+    std::string result;
+    
+    if(is_date_format(format.value))
     {
-        return std::to_string(static_cast<long long int>(number));
+        const std::string date_unquoted = ",-/: ";
+        
+        const std::vector<std::string> dates =
+        {
+            "m",
+            "mm",
+            "mmm",
+            "mmmmm",
+            "mmmmmm",
+            "d",
+            "dd",
+            "ddd",
+            "dddd",
+            "yy",
+            "yyyy"
+            "h",
+            "[h]",
+            "hh",
+            "m",
+            "[m]",
+            "mm",
+            "s",
+            "[s]",
+            "ss",
+            "AM/PM",
+            "am/pm",
+            "A/P",
+            "a/p"
+        };
+        
+        auto split = split_string_any(format.value, date_unquoted);
+        std::string::size_type index = 0, prev = 0;
+        auto d = xlnt::datetime::from_number(number, base_date);
+        bool processed_month = false;
+        
+        for(auto part : split)
+        {
+            while(format.value.substr(index, part.size()) != part)
+            {
+                index++;
+            }
+            
+            auto between = format.value.substr(prev, index - prev);
+            result.append(between);
+            
+            if(part == "m" && !processed_month)
+            {
+                result.append(std::to_string(d.month));
+                processed_month = true;
+            }
+            if(part == "mm" && !processed_month)
+            {
+                if(d.month < 10)
+                {
+                    result.append("0");
+                }
+                
+                result.append(std::to_string(d.month));
+                processed_month = true;
+            }
+            if(part == "mmm" && !processed_month)
+            {
+                result.append(MonthNames.at(d.month - 1).substr(0, 3));
+                processed_month = true;
+            }
+            if(part == "mmmm" && !processed_month)
+            {
+                result.append(MonthNames.at(d.month - 1));
+                processed_month = true;
+            }
+            if(part == "d")
+            {
+                result.append(std::to_string(d.day));
+            }
+            if(part == "dd")
+            {
+                if(d.day < 10)
+                {
+                    result.append("0");
+                }
+                
+                result.append(std::to_string(d.day));
+            }
+            if(part == "yyyy")
+            {
+                result.append(std::to_string(d.year));
+            }
+            
+            if(part == "h")
+            {
+                result.append(std::to_string(d.hour));
+                processed_month = true;
+            }
+            if(part == "hh")
+            {
+                if(d.hour < 10)
+                {
+                    result.append("0");
+                }
+                
+                result.append(std::to_string(d.hour));
+                processed_month = true;
+            }
+            if(part == "m")
+            {
+                result.append(std::to_string(d.minute));
+            }
+            if(part == "mm")
+            {
+                if(d.minute < 10)
+                {
+                    result.append("0");
+                }
+                
+                result.append(std::to_string(d.minute));
+            }
+            if(part == "s")
+            {
+                result.append(std::to_string(d.second));
+            }
+            if(part == "ss")
+            {
+                if(d.second < 10)
+                {
+                    result.append("0");
+                }
+                
+                result.append(std::to_string(d.second));
+            }
+            
+            
+            
+            index += part.size();
+            prev = index;
+        }
+        
+        if(index < format.value.size())
+        {
+            result.append(format.value.substr(index));
+        }
+    }
+    else if(number == static_cast<long long int>(number))
+    {
+        result = std::to_string(static_cast<long long int>(number));
+    }
+    else
+    {
+        result = std::to_string(number);
     }
     
-    return std::to_string(number);
+    return result;
 }
 
 std::string format_section(const std::string &text, const section &format)
@@ -334,21 +530,21 @@ std::string format_section(const std::string &text, const section &format)
     return first_part + middle_part + last_part;
 }
 
-std::string format_number(long double number, const std::string &format)
+std::string format_number(long double number, const std::string &format, xlnt::calendar base_date)
 {
     auto sections = parse_format_sections(format);
     
     if(number > 0)
     {
-        return format_section(number, sections.first);
+        return format_section(number, sections.first, base_date);
     }
     else if(number < 0)
     {
-        return format_section(number, sections.second);
+        return format_section(number, sections.second, base_date);
     }
     
     // number == 0
-    return format_section(number, sections.third);
+    return format_section(number, sections.third, base_date);
 }
 
 std::string format_text(const std::string &text, const std::string &format)
@@ -358,12 +554,6 @@ std::string format_text(const std::string &text, const std::string &format)
     return format_section(text, sections.fourth);
 }
 
-bool is_date_format(const std::string &format_string)
-{
-    auto not_in = format_string.find_first_not_of("/-:, mMyYdDhHsS");
-    return not_in == std::string::npos;
-}
-
 }
 
 namespace xlnt {
@@ -411,7 +601,6 @@ bool cell::garbage_collectible() const
 template<>
 void cell::set_value(bool b)
 {
-    d_->is_date_ = false;
     d_->value_numeric_ = b ? 1 : 0;
     d_->type_ = type::boolean;
 }
@@ -419,7 +608,6 @@ void cell::set_value(bool b)
 template<>
 void cell::set_value(std::int8_t i)
 {
-    d_->is_date_ = false;
     d_->value_numeric_ = static_cast<long double>(i);
     d_->type_ = type::numeric;
 }
@@ -427,7 +615,6 @@ void cell::set_value(std::int8_t i)
 template<>
 void cell::set_value(std::int16_t i)
 {
-    d_->is_date_ = false;
     d_->value_numeric_ = static_cast<long double>(i);
     d_->type_ = type::numeric;
 }
@@ -435,7 +622,6 @@ void cell::set_value(std::int16_t i)
 template<>
 void cell::set_value(std::int32_t i)
 {
-    d_->is_date_ = false;
     d_->value_numeric_ = static_cast<long double>(i);
     d_->type_ = type::numeric;
 }
@@ -443,7 +629,6 @@ void cell::set_value(std::int32_t i)
 template<>
 void cell::set_value(std::int64_t i)
 {
-    d_->is_date_ = false;
     d_->value_numeric_ = static_cast<long double>(i);
     d_->type_ = type::numeric;
 }
@@ -451,7 +636,6 @@ void cell::set_value(std::int64_t i)
 template<>
 void cell::set_value(std::uint8_t i)
 {
-    d_->is_date_ = false;
     d_->value_numeric_ = static_cast<long double>(i);
     d_->type_ = type::numeric;
 }
@@ -459,7 +643,6 @@ void cell::set_value(std::uint8_t i)
 template<>
 void cell::set_value(std::uint16_t i)
 {
-    d_->is_date_ = false;
     d_->value_numeric_ = static_cast<long double>(i);
     d_->type_ = type::numeric;
 }
@@ -467,7 +650,6 @@ void cell::set_value(std::uint16_t i)
 template<>
 void cell::set_value(std::uint32_t i)
 {
-    d_->is_date_ = false;
     d_->value_numeric_ = static_cast<long double>(i);
     d_->type_ = type::numeric;
 }
@@ -475,7 +657,6 @@ void cell::set_value(std::uint32_t i)
 template<>
 void cell::set_value(std::uint64_t i)
 {
-    d_->is_date_ = false;
     d_->value_numeric_ = static_cast<long double>(i);
     d_->type_ = type::numeric;
 }
@@ -484,7 +665,6 @@ void cell::set_value(std::uint64_t i)
 template<>
 void cell::set_value(unsigned long i)
 {
-    d_->is_date_ = false;
     d_->value_numeric_ = static_cast<long double>(i);
     d_->type_ = type::numeric;
 }
@@ -494,7 +674,6 @@ void cell::set_value(unsigned long i)
 template<>
 void cell::set_value(long long i)
 {
-    d_->is_date_ = false;
     d_->value_numeric_ = static_cast<long double>(i);
     d_->type_ = type::numeric;
 }
@@ -502,7 +681,6 @@ void cell::set_value(long long i)
 template<>
 void cell::set_value(unsigned long long i)
 {
-    d_->is_date_ = false;
     d_->value_numeric_ = static_cast<long double>(i);
     d_->type_ = type::numeric;
 }
@@ -511,7 +689,6 @@ void cell::set_value(unsigned long long i)
 template<>
 void cell::set_value(float f)
 {
-    d_->is_date_ = false;
     d_->value_numeric_ = static_cast<long double>(f);
     d_->type_ = type::numeric;
 }
@@ -519,7 +696,6 @@ void cell::set_value(float f)
 template<>
 void cell::set_value(double d)
 {
-    d_->is_date_ = false;
     d_->value_numeric_ = static_cast<long double>(d);
     d_->type_ = type::numeric;
 }
@@ -527,7 +703,6 @@ void cell::set_value(double d)
 template<>
 void cell::set_value(long double d)
 {
-    d_->is_date_ = false;
     d_->value_numeric_ = static_cast<long double>(d);
     d_->type_ = type::numeric;
 }
@@ -550,44 +725,43 @@ void cell::set_value(cell c)
     d_->type_ = c.d_->type_;
     d_->value_numeric_ = c.d_->value_numeric_;
     d_->value_string_ = c.d_->value_string_;
-    d_->is_date_ = c.d_->is_date_;
     d_->hyperlink_ = c.d_->hyperlink_;
     d_->has_hyperlink_ = c.d_->has_hyperlink_;
     d_->formula_ = c.d_->formula_;
-    set_style(c.get_style());
+    d_->style_id_ = c.d_->style_id_;
     set_comment(c.get_comment());
 }
     
 template<>
 void cell::set_value(date d)
 {
-    auto base_date = get_parent().get_parent().get_properties().excel_base_date;
-    d_->set_date(d.to_number(base_date), xlnt::number_format::format::date_yyyymmdd2);
+    d_->type_ = type::numeric;
+    d_->value_numeric_ = d.to_number(get_base_date());
+    set_number_format(number_format(number_format::format::date_yyyymmdd2));
 }
 
 template<>
 void cell::set_value(datetime d)
 {
-    auto base_date = get_parent().get_parent().get_properties().excel_base_date;
-    d_->set_date(d.to_number(base_date), xlnt::number_format::format::date_datetime);
+    d_->type_ = type::numeric;
+    d_->value_numeric_ = d.to_number(get_base_date());
+    set_number_format(number_format(number_format::format::date_datetime));
 }
 
 template<>
 void cell::set_value(time t)
 {
-    d_->set_date(t.to_number(), xlnt::number_format::format::date_time6);
+    d_->type_ = type::numeric;
+    d_->value_numeric_ = t.to_number();
+    set_number_format(number_format(number_format::format::date_time6));
 }
 
 template<>
 void cell::set_value(timedelta t)
 {
-    d_->set_date(t.to_number(), xlnt::number_format::format::date_timedelta);
-    d_->is_date_ = false; // a timedelta isn't actually a date, still uses mostly the same code
-}
-    
-bool cell::has_style() const
-{
-    return d_->style_ != nullptr;
+    d_->type_ = type::numeric;
+    d_->value_numeric_ = t.to_number();
+    set_number_format(number_format(number_format::format::date_timedelta));
 }
 
 row_t cell::get_row() const
@@ -612,9 +786,9 @@ bool cell::is_merged() const
 
 bool cell::is_date() const
 {
-    if(get_data_type() == type::numeric && has_style())
+    if(get_data_type() == type::numeric)
     {
-        auto number_format = get_style().get_number_format().get_format_code_string();
+        auto number_format = get_number_format().get_format_string();
         
         if(number_format != "General")
         {
@@ -648,21 +822,6 @@ bool cell::operator==(const cell &comparand) const
     return d_ == comparand.d_;
 }
 
-style &cell::get_style()
-{
-    return d_->get_style(true);
-}
-
-const style &cell::get_style() const
-{
-    return d_->get_style();
-}
-    
-void cell::set_style(const xlnt::style &s)
-{
-    get_style() = s;
-}
-
 cell &cell::operator=(const cell &rhs)
 {
     *d_ = *rhs.d_;
@@ -874,54 +1033,44 @@ std::size_t cell::get_xf_index() const
     return d_->xf_index_;
 }
 
-std::string cell::get_number_format()
+const number_format &cell::get_number_format() const
 {
-    return get_style().get_number_format().get_format_code_string();
+    return get_parent().get_parent().get_number_format(d_->style_id_);
 }
     
-std::string cell::get_number_format() const
+const font &cell::get_font() const
 {
-    return get_style().get_number_format().get_format_code_string();
-}
-
-font &cell::get_font()
-{
-    return get_style().get_font();
+    return get_parent().get_parent().get_font(d_->style_id_);
 }
     
-fill &cell::get_fill()
-{
-    return get_style().get_fill();
-}
-
 const fill &cell::get_fill() const
 {
-    return get_style().get_fill();
+    return get_parent().get_parent().get_fill(d_->style_id_);
 }
 
-border &cell::get_border()
+const border &cell::get_border() const
 {
-    return get_style().get_border();
+    return get_parent().get_parent().get_border(d_->style_id_);
 }
 
-alignment &cell::get_alignment()
+const alignment &cell::get_alignment() const
 {
-    return get_style().get_alignment();
+    return get_parent().get_parent().get_alignment(d_->style_id_);
 }
 
-protection &cell::get_protection()
+const protection &cell::get_protection() const
 {
-    return get_style().get_protection();
+    return get_parent().get_parent().get_protection(d_->style_id_);
 }
 
-bool cell::pivot_button()
+bool cell::pivot_button() const
 {
-    return get_style().pivot_button();
+    return get_parent().get_parent().get_pivot_button(d_->style_id_);
 }
 
-bool cell::quote_prefix()
+bool cell::quote_prefix() const
 {
-    return get_style().quote_prefix();
+    return get_parent().get_parent().get_quote_prefix(d_->style_id_);
 }
     
 void cell::clear_value()
@@ -1021,25 +1170,24 @@ time cell::get_value() const
 template<>
 datetime cell::get_value() const
 {
-    return datetime::from_number(d_->value_numeric_, xlnt::calendar::windows_1900);
+    return datetime::from_number(d_->value_numeric_, get_base_date());
 }
 
 template<>
 date cell::get_value() const
 {
-    return date::from_number(static_cast<int>(d_->value_numeric_), xlnt::calendar::windows_1900);
+    return date::from_number(static_cast<int>(d_->value_numeric_), get_base_date());
 }
 
 template<>
 timedelta cell::get_value() const
 {
-    return timedelta(0, 0);
-    //return timedelta::from_number(d_->value_numeric_);
+    return timedelta::from_number(d_->value_numeric_);
 }
 
-void cell::set_number_format(const std::string &format_string, int index)
+void cell::set_number_format(const number_format &number_format_)
 {
-    get_style().get_number_format().set_format_code_string(format_string, index);
+    d_->style_id_ = get_parent().get_parent().set_number_format(number_format_, d_->style_id_);
 }
 
 template<>
@@ -1055,28 +1203,33 @@ bool cell::has_value() const
 
 std::string cell::to_string() const
 {
-    std::string number_format = "General";
-    
-    if(has_style())
-    {
-        number_format = get_style().get_number_format().get_format_code_string();
-    }
+    auto nf = get_number_format();
     
     switch(get_data_type())
     {
         case cell::type::null:
             return "";
         case cell::type::numeric:
-            return format_number(get_value<long double>(), number_format);
+            return format_number(get_value<long double>(), nf.get_format_string(), get_base_date());
         case cell::type::string:
         case cell::type::formula:
         case cell::type::error:
-            return format_text(get_value<std::string>(), number_format);
+            return format_text(get_value<std::string>(), nf.get_format_string());
         case cell::type::boolean:
             return get_value<long double>() == 0 ? "FALSE" : "TRUE";
 		default:
 			return "";
     }
 }
+    
+std::size_t cell::get_style_id() const
+{
+    return d_->style_id_;
+}
+    
+calendar cell::get_base_date() const
+{
+    return get_parent().get_parent().get_properties().excel_base_date;
+}
 
 } // namespace xlnt
diff --git a/source/datetime.cpp b/source/datetime.cpp
index 74319d96..4a546c75 100644
--- a/source/datetime.cpp
+++ b/source/datetime.cpp
@@ -186,5 +186,10 @@ double timedelta::to_number() const
 {
     return days + hours / 24.0;
 }
-    
+
+timedelta timedelta::from_number(long double number)
+{
+    return timedelta(static_cast<long long int>(number), 0);
+}
+
 } // namespace xlnt
diff --git a/source/detail/cell_impl.cpp b/source/detail/cell_impl.cpp
index 6b3194e0..01ce3a01 100644
--- a/source/detail/cell_impl.cpp
+++ b/source/detail/cell_impl.cpp
@@ -5,30 +5,6 @@
 
 namespace xlnt {
 namespace detail {
-
-    
-    cell::type type_;
-    
-    worksheet_impl *parent_;
-    
-    column_t column_;
-    row_t row_;
-    
-    std::string value_string_;
-    long double value_numeric_;
-    
-    std::string formula_;
-    
-    bool has_hyperlink_;
-    relationship hyperlink_;
-    
-    bool is_merged_;
-    bool is_date_;
-    
-    std::size_t xf_index_;
-    
-    std::unique_ptr<style> style_;
-    std::unique_ptr<comment_impl> comment_;
     
 cell_impl::cell_impl() : cell_impl(1, 1)
 {
@@ -46,9 +22,8 @@ cell_impl::cell_impl(worksheet_impl *parent, column_t column, row_t row)
       value_numeric_(0),
       has_hyperlink_(false),
       is_merged_(false),
-      is_date_(false),
       xf_index_(0),
-      style_(nullptr),
+      style_id_(1),
       comment_(nullptr)
 {
 }
@@ -68,14 +43,9 @@ cell_impl &cell_impl::operator=(const cell_impl &rhs)
     column_ = rhs.column_;
     row_ = rhs.row_;
     is_merged_ = rhs.is_merged_;
-    is_date_ = rhs.is_date_;
     has_hyperlink_ = rhs.has_hyperlink_;
     type_ = rhs.type_;
-    
-    if(rhs.style_ != nullptr)
-    {
-        style_.reset(new style(*rhs.style_));
-    }
+    style_id_ = rhs.style_id_;
     
     if(rhs.comment_ != nullptr)
     {
diff --git a/source/detail/cell_impl.hpp b/source/detail/cell_impl.hpp
index b67770fc..bcf507ab 100644
--- a/source/detail/cell_impl.hpp
+++ b/source/detail/cell_impl.hpp
@@ -8,6 +8,7 @@
 #include <xlnt/common/datetime.hpp>
 #include <xlnt/common/types.hpp>
 #include <xlnt/common/relationship.hpp>
+#include <xlnt/styles/number_format.hpp>
 
 #include "comment_impl.hpp"
 
@@ -123,37 +124,13 @@ struct cell_impl
     cell_impl(const cell_impl &rhs);
     cell_impl &operator=(const cell_impl &rhs);
     
-    style &get_style(bool create_if_null)
+    cell self()
     {
-        if(style_ == nullptr && create_if_null)
-        {
-            style_.reset(new style());
-        }
-        
-        return *style_;
-    }
-    
-    const style &get_style() const
-    {
-        if(style_ == nullptr)
-        {
-            throw std::runtime_error("call has_style to check if const cell has a style before accessing it");
-        }
-        
-        return *style_;
-    }
-
-    void set_date(long double number, xlnt::number_format::format format_code)
-    {
-        is_date_ = true;
-        get_style(true).get_number_format().set_format_code(format_code);
-        value_numeric_ = number;
-        type_ = cell::type::numeric;
+        return xlnt::cell(this);
     }
     
     void set_string(const std::string &s, bool guess_types)
     {
-        is_date_ = false;
         value_string_ = check_string(s);
         type_ = cell::type::string;
         
@@ -175,7 +152,7 @@ struct cell_impl
             {
                 value_numeric_ = percentage.second;
                 type_ = cell::type::numeric;
-                get_style(true).get_number_format().set_format_code(xlnt::number_format::format::percentage);
+                self().set_number_format(xlnt::number_format(xlnt::number_format::format::percentage));
             }
             else
             {
@@ -183,7 +160,9 @@ struct cell_impl
                 
                 if (time.first)
                 {
-                    set_date(time.second.to_number(), xlnt::number_format::format::date_time6);
+                    type_ = cell::type::numeric;
+                    self().set_number_format(xlnt::number_format(number_format::format::date_time6));
+                    value_numeric_ = time.second.to_number();
                 }
                 else
                 {
@@ -215,11 +194,10 @@ struct cell_impl
     relationship hyperlink_;
     
     bool is_merged_;
-    bool is_date_;
     
     std::size_t xf_index_;
+    std::size_t style_id_;
     
-    std::unique_ptr<style> style_;
     std::unique_ptr<comment_impl> comment_;
 };
     
diff --git a/source/detail/workbook_impl.hpp b/source/detail/workbook_impl.hpp
index 7da56c62..cd956dfa 100644
--- a/source/detail/workbook_impl.hpp
+++ b/source/detail/workbook_impl.hpp
@@ -17,7 +17,22 @@ struct workbook_impl
         drawings_(other.drawings_), 
         properties_(other.properties_), 
         guess_types_(other.guess_types_),
-        data_only_(other.data_only_)
+        data_only_(other.data_only_),
+        next_style_id_(other.next_style_id_),
+        alignments_(other.alignments_),
+    borders_(other.borders_),
+    fills_(other.fills_),
+    fonts_(other.fonts_),
+    number_formats_(other.number_formats_),
+    protections_(other.protections_),
+    style_alignment_(other.style_alignment_),
+    style_border_(other.style_border_),
+    style_fill_(other.style_fill_),
+    style_font_(other.style_font_),
+    style_number_format_(other.style_number_format_),
+    style_protection_(other.style_protection_),
+    style_pivot_button_(other.style_pivot_button_),
+    style_quote_prefix_(other.style_quote_prefix_)
     {
     }
     
@@ -33,6 +48,21 @@ struct workbook_impl
         properties_ = other.properties_;
         guess_types_ = other.guess_types_;
         data_only_ = other.data_only_;
+        next_style_id_ = other.next_style_id_;
+        alignments_ = other.alignments_;
+        borders_ = other.borders_;
+        fills_ = other.fills_;
+        fonts_ = other.fonts_;
+        number_formats_ = other.number_formats_;
+        protections_ = other.protections_;
+        style_alignment_ = other.style_alignment_;
+        style_border_ = other.style_border_;
+        style_fill_ = other.style_fill_;
+        style_font_ = other.style_font_;
+        style_number_format_ = other.style_number_format_;
+        style_protection_ = other.style_protection_;
+        style_pivot_button_ = other.style_pivot_button_;
+        style_quote_prefix_ = other.style_quote_prefix_;
         
         return *this;
     }
@@ -44,6 +74,22 @@ struct workbook_impl
     document_properties properties_;
     bool guess_types_;
     bool data_only_;
+    
+    std::size_t next_style_id_;
+    std::unordered_map<std::size_t, alignment> alignments_;
+    std::unordered_map<std::size_t, border> borders_;
+    std::unordered_map<std::size_t, fill> fills_;
+    std::unordered_map<std::size_t, font> fonts_;
+    std::unordered_map<std::size_t, number_format> number_formats_;
+    std::unordered_map<std::size_t, protection> protections_;
+    std::unordered_map<std::size_t, std::size_t> style_alignment_;
+    std::unordered_map<std::size_t, std::size_t> style_border_;
+    std::unordered_map<std::size_t, std::size_t> style_fill_;
+    std::unordered_map<std::size_t, std::size_t> style_font_;
+    std::unordered_map<std::size_t, std::size_t> style_number_format_;
+    std::unordered_map<std::size_t, std::size_t> style_protection_;
+    std::unordered_map<std::size_t, bool> style_pivot_button_;
+    std::unordered_map<std::size_t, bool> style_quote_prefix_;
 };
 
 } // namespace detail
diff --git a/source/number_format.cpp b/source/number_format.cpp
index 57ebd83f..35f97446 100644
--- a/source/number_format.cpp
+++ b/source/number_format.cpp
@@ -123,7 +123,21 @@ const std::unordered_map<std::string, int> &number_format::reversed_builtin_form
     
     return formats;
 }
-    
+
+number_format::number_format() : number_format(format::general)
+{
+}
+
+number_format::number_format(format code) : format_code_(code), format_index_(0)
+{
+    set_format_code(code);
+}
+
+number_format::number_format(const std::string &format_string) : number_format(format::general)
+{
+    set_format_string(format_string);
+}
+
 number_format::format number_format::lookup_format(int code)
 {
     if(builtin_formats().find(code) == builtin_formats().end())
@@ -142,14 +156,58 @@ number_format::format number_format::lookup_format(int code)
     return match->first;
 }
 
-std::string number_format::get_format_code_string() const
+std::string number_format::get_format_string() const
 {
-    if(builtin_formats().find(format_index_) == builtin_formats().end())
-    {
-        return custom_format_code_;
-    }
+    return format_string_;
+}
+
+number_format::format number_format::get_format_code() const
+{
+    return format_code_;
+}
+
+std::size_t number_format::hash() const
+{
+    std::hash<std::string> hasher;
+    return hasher(format_string_);
+}
     
-    return builtin_formats().at(format_index_);
+void number_format::set_format_string(const std::string &format_string)
+{
+    format_string_ = format_string;
+    format_index_ = -1;
+    format_code_ = format::unknown;
+    
+    const auto &reversed = reversed_builtin_formats();
+    
+    if(reversed.find(format_string) != reversed.end())
+    {
+        format_index_ = reversed.at(format_string);
+        
+        for(const auto &pair : format_strings())
+        {
+            if(pair.second == format_string)
+            {
+                format_code_ = pair.first;
+                break;
+            }
+        }
+    }
+}
+
+void number_format::set_format_code(xlnt::number_format::format format_code)
+{
+    format_code_ = format_code;
+    format_string_ = format_strings().at(format_code);
+    
+    try
+    {
+        format_index_ = reversed_builtin_formats().at(format_string_);
+    }
+    catch(std::out_of_range)
+    {
+        format_index_ = -1;
+    }
 }
 
 } // namespace xlnt
diff --git a/source/reader.cpp b/source/reader.cpp
index a93ad82b..a619dadd 100644
--- a/source/reader.cpp
+++ b/source/reader.cpp
@@ -12,6 +12,7 @@
 #include <xlnt/workbook/workbook.hpp>
 #include <xlnt/worksheet/range_reference.hpp>
 #include <xlnt/worksheet/worksheet.hpp>
+#include <xlnt/styles/number_format.hpp>
 
 namespace {
 
@@ -164,20 +165,16 @@ void read_worksheet_common(xlnt::worksheet ws, const pugi::xml_node &root_node,
                             
                             if(match != custom_number_formats.end())
                             {
-                                ws.get_cell(address).get_style().get_number_format().set_format_code_string(match->second, number_format_id);
+                                xlnt::number_format nf(match->second);
+                                auto cell = ws.get_cell(address);
+                                cell.set_number_format(nf);
                             }
                         }
                         else
                         {
-                            ws.get_cell(address).get_style().get_number_format().set_format_code(format);
-                        }
-                        
-                        //TODO: this is bad
-                        if(ws.get_cell(address).get_style().get_number_format().get_format_code_string().find_first_of("mdyhs") != std::string::npos)
-                        {
-                            auto base_date = ws.get_parent().get_properties().excel_base_date;
-                            auto converted = xlnt::datetime::from_number(std::stold(value_string), base_date);
-                            ws.get_cell(address).set_value(converted.to_number(xlnt::calendar::windows_1900));
+                            xlnt::number_format nf(format);
+                            auto cell = ws.get_cell(address);
+                            cell.set_number_format(nf);
                         }
                     }
                 }
diff --git a/source/style.cpp b/source/style.cpp
index 46642b59..1c1bf7ce 100644
--- a/source/style.cpp
+++ b/source/style.cpp
@@ -1,69 +1,92 @@
+#include <xlnt/cell/cell.hpp>
 #include <xlnt/styles/style.hpp>
 
+#include "font.hpp"
+#include "number_format.hpp"
+#include "protection.hpp"
+
+namespace {
+
+template <class T>
+void hash_combine(std::size_t& seed, const T& v)
+{
+    std::hash<T> hasher;
+    seed ^= hasher(v) + 0x9e3779b9 + (seed<<6) + (seed>>2);
+}
+    
+}
+
 namespace xlnt {
 
-style::style(const style &rhs) : number_format_(rhs.number_format_), protection_(rhs.protection_)
+style::style()
 {
 }
 
-void style::set_protection(xlnt::protection protection)
+style::style(const style &other)
 {
-    protection_ = protection;
+}
+
+const cell style::get_parent() const
+{
+    return cell(parent_);
+}
+
+std::size_t style::hash() const
+{
+    std::size_t seed = 100;
+    std::hash<std::string> string_hash;
+    auto font_ = get_font();
+    hash_combine(seed, string_hash(font_.name_));
+    hash_combine(seed, font_.size_);
+    hash_combine(seed, static_cast<std::size_t>(font_.underline_));
+    std::size_t bools = font_.bold_;
+    bools = bools << 1 & font_.italic_;
+    bools = bools << 1 & font_.strikethrough_;
+    bools = bools << 1 & font_.superscript_;
+    bools = bools << 1 & font_.subscript_;
+    hash_combine(seed, bools);
+    
+    return seed;
+}
+
+const number_format &style::get_number_format() const
+{
+    return get_parent().get_number_format();
+}
+
+const border &style::get_border() const
+{
+    return get_parent().get_border();
+}
+
+const alignment &style::get_alignment() const
+{
+    return get_parent().get_alignment();
 }
     
-void style::set_number_format(xlnt::number_format format)
-{
-    number_format_ = format;
-}
-
-border &style::get_border()
-{
-    return border_;
-}
-
-bool style::pivot_button()
-{
-    return pivot_button_;
-}
-
-bool style::quote_prefix()
-{
-    return quote_prefix_;
-}
-
-alignment &style::get_alignment()
-{
-    return alignment_;
-}
-    
-fill &style::get_fill()
-{
-    return fill_;
-}
-
 const fill &style::get_fill() const
 {
-    return fill_;
+    return get_parent().get_fill();
 }
 
-font &style::get_font()
+const font &style::get_font() const
 {
-    return font_;
+    return get_parent().get_font();
 }
 
-protection &style::get_protection()
+const protection &style::get_protection() const
 {
-    return protection_;
+    return get_parent().get_protection();
 }
 
-void style::set_pivot_button(bool pivot)
+bool style::pivot_button() const
 {
-    pivot_button_ = pivot;
+    return get_parent().pivot_button();
 }
 
-void style::set_quote_prefix(bool quote)
+bool style::quote_prefix() const
 {
-    quote_prefix_ = quote;
+    return get_parent().quote_prefix();
 }
 
 } // namespace xlnt
diff --git a/source/style_writer.cpp b/source/style_writer.cpp
index b345d07b..7719f02e 100644
--- a/source/style_writer.cpp
+++ b/source/style_writer.cpp
@@ -1,6 +1,12 @@
 #include <sstream>
 #include <pugixml.hpp>
 
+#include <xlnt/styles/alignment.hpp>
+#include <xlnt/styles/borders.hpp>
+#include <xlnt/styles/fill.hpp>
+#include <xlnt/styles/font.hpp>
+#include <xlnt/styles/number_format.hpp>
+#include <xlnt/styles/protection.hpp>
 #include <xlnt/writer/style_writer.hpp>
 #include <xlnt/workbook/workbook.hpp>
 #include <xlnt/worksheet/worksheet.hpp>
@@ -14,46 +20,6 @@ style_writer::style_writer(xlnt::workbook &wb) : wb_(wb)
   
 }
 
-std::unordered_map<std::size_t, std::string> style_writer::get_style_by_hash() const
-{
-    std::unordered_map<std::size_t, std::string> styles;
-    for(auto ws : wb_)
-    {
-        for(auto row : ws.rows())
-        {
-            for(auto cell : row)
-            {
-                if(cell.has_style())
-                {
-                    styles[1] = "style";
-                }
-            }
-        }
-    }
-    return styles;
-}
-
-std::vector<style> style_writer::get_styles() const
-{
-    std::vector<style> styles;
-    
-    for(auto ws : wb_)
-    {
-        for(auto row : ws.rows())
-        {
-            for(auto cell : row)
-            {
-                if(cell.has_style())
-                {
-                    styles.push_back(cell.get_style());
-                }
-            }
-        }
-    }
-    
-    return styles;
-}
-    
 std::string style_writer::write_table() const
 {
     pugi::xml_document doc;
@@ -62,36 +28,53 @@ std::string style_writer::write_table() const
     style_sheet_node.append_attribute("xmlns:mc").set_value("http://schemas.openxmlformats.org/markup-compatibility/2006");
     style_sheet_node.append_attribute("mc:Ignorable").set_value("x14ac");
     style_sheet_node.append_attribute("xmlns:x14ac").set_value("http://schemas.microsoft.com/office/spreadsheetml/2009/9/ac");
-
-    std::vector<style> custom_styles;
-    for(auto style : get_styles())
+    
+    auto num_fmts_node = style_sheet_node.append_child("numFmts");
+    auto &num_fmts = wb_.get_number_formats();
+    num_fmts_node.append_attribute("count").set_value(static_cast<int>(num_fmts.size()));
+    int custom_index = 164;
+    
+    for(auto &num_fmt : num_fmts)
     {
-        if((int)style.get_number_format().get_format_code() > 163)
+        auto num_fmt_node = num_fmts_node.append_child("numFmt");
+        
+        if(num_fmt.second.get_format_code() == number_format::format::unknown)
         {
-            custom_styles.push_back(style);
+            num_fmt_node.append_attribute("numFmtId").set_value(custom_index++);
         }
-    }
-
-    if(!custom_styles.empty())
-    {
-
+        else
+        {
+            num_fmt_node.append_attribute("numFmtId").set_value(num_fmt.second.get_format_index());
+        }
+                                                                
+        num_fmt_node.append_attribute("formatCode").set_value("General");
     }
 
     auto fonts_node = style_sheet_node.append_child("fonts");
-    fonts_node.append_attribute("count").set_value(1);
+    auto &fonts = wb_.get_fonts();
+    fonts_node.append_attribute("count").set_value(static_cast<int>(fonts.size()));
     fonts_node.append_attribute("x14ac:knownFonts").set_value(1);
-
-    auto font_node = fonts_node.append_child("font");
-    auto size_node = font_node.append_child("sz");
-    size_node.append_attribute("val").set_value(11);
-    auto color_node = font_node.append_child("color");
-    color_node.append_attribute("theme").set_value(1);
-    auto name_node = font_node.append_child("name");
-    name_node.append_attribute("val").set_value("Calibri");
-    auto family_node = font_node.append_child("family");
-    family_node.append_attribute("val").set_value(2);
-    auto scheme_node = font_node.append_child("scheme");
-    scheme_node.append_attribute("val").set_value("minor");
+    
+    for(auto &f : fonts)
+    {
+        auto font_node = fonts_node.append_child("font");
+        auto size_node = font_node.append_child("sz");
+        size_node.append_attribute("val").set_value(f.second.get_size());
+        auto color_node = font_node.append_child("color");
+        color_node.append_attribute("theme").set_value(1);
+        auto name_node = font_node.append_child("name");
+        name_node.append_attribute("val").set_value(f.second.get_name().c_str());
+        auto family_node = font_node.append_child("family");
+        family_node.append_attribute("val").set_value(2);
+        auto scheme_node = font_node.append_child("scheme");
+        scheme_node.append_attribute("val").set_value("minor");
+        
+        if(f.second.is_bold())
+        {
+            auto bold_node = font_node.append_child("b");
+            bold_node.append_attribute("val").set_value(1);
+        }
+    }
 
     auto fills_node = style_sheet_node.append_child("fills");
     fills_node.append_attribute("count").set_value(2);
diff --git a/source/workbook.cpp b/source/workbook.cpp
index 79744b55..fa5b9de0 100644
--- a/source/workbook.cpp
+++ b/source/workbook.cpp
@@ -13,6 +13,12 @@
 #include <xlnt/common/zip_file.hpp>
 #include <xlnt/drawing/drawing.hpp>
 #include <xlnt/reader/reader.hpp>
+#include <xlnt/styles/alignment.hpp>
+#include <xlnt/styles/borders.hpp>
+#include <xlnt/styles/fill.hpp>
+#include <xlnt/styles/font.hpp>
+#include <xlnt/styles/number_format.hpp>
+#include <xlnt/styles/protection.hpp>
 #include <xlnt/workbook/document_properties.hpp>
 #include <xlnt/workbook/named_range.hpp>
 #include <xlnt/workbook/workbook.hpp>
@@ -56,9 +62,8 @@ static std::string create_temporary_filename()
 namespace xlnt {
 namespace detail {
 
-workbook_impl::workbook_impl() : active_sheet_index_(0), guess_types_(false), data_only_(false)
+workbook_impl::workbook_impl() : active_sheet_index_(0), guess_types_(false), data_only_(false), next_style_id_(0)
 {
-    
 }
 
 } // namespace detail
@@ -69,6 +74,14 @@ workbook::workbook() : d_(new detail::workbook_impl())
     create_relationship("rId2", "sharedStrings.xml", relationship::type::shared_strings);
     create_relationship("rId3", "styles.xml", relationship::type::styles);
     create_relationship("rId4", "theme/theme1.xml", relationship::type::theme);
+    set_alignment(alignment(), 1);
+    set_border(border(), 1);
+    set_fill(fill(), 1);
+    set_font(font(), 1);
+    set_number_format(number_format(), 1);
+    set_protection(protection(), 1);
+    d_->style_pivot_button_[1] = false;
+    d_->style_quote_prefix_[1] = false;
 }
 
 workbook::iterator::iterator(workbook &wb, std::size_t index) : wb_(wb), index_(index)
@@ -657,64 +670,242 @@ void workbook::set_data_only(bool data_only)
 {
     d_->data_only_ = data_only;
 }
+
+void workbook::add_border(xlnt::border /*b*/)
+{
     
-    void workbook::add_border(xlnt::border /*b*/)
-    {
-        
-    }
-    
-    void workbook::add_alignment(xlnt::alignment /*a*/)
-    {
-        
-    }
-    
-    void workbook::add_protection(xlnt::protection /*p*/)
-    {
-        
-    }
-    
-    void workbook::add_number_format(const std::string &/*format*/)
-    {
-        
-    }
-    
-    void workbook::add_fill(xlnt::fill &/*f*/)
-    {
-        
-    }
-    
-    void workbook::add_font(xlnt::font /*f*/)
-    {
-        
-    }
-    
-    void workbook::set_code_name(const std::string &/*code_name*/)
-    {
-        
-    }
-    
-    bool workbook::has_loaded_theme()
-    {
-        return false;
-    }
-    
-    std::string workbook::get_loaded_theme()
-    {
-        return "";
-    }
-    
-    std::vector<named_range> workbook::get_named_ranges() const
-    {
-        std::vector<named_range> named_ranges;
-        
-        for(auto ws : *this)
-        {
-            for(auto &ws_named_range : ws.d_->named_ranges_)
-            {
-                named_ranges.push_back(ws_named_range.second);
-            }
-        }
-        
-        return named_ranges;
-    }
 }
+
+void workbook::add_alignment(xlnt::alignment /*a*/)
+{
+    
+}
+
+void workbook::add_protection(xlnt::protection /*p*/)
+{
+    
+}
+
+void workbook::add_number_format(const std::string &/*format*/)
+{
+    
+}
+
+void workbook::add_fill(xlnt::fill &/*f*/)
+{
+    
+}
+
+void workbook::add_font(xlnt::font /*f*/)
+{
+    
+}
+
+void workbook::set_code_name(const std::string &/*code_name*/)
+{
+    
+}
+
+bool workbook::has_loaded_theme()
+{
+    return false;
+}
+
+std::string workbook::get_loaded_theme()
+{
+    return "";
+}
+
+std::vector<named_range> workbook::get_named_ranges() const
+{
+    std::vector<named_range> named_ranges;
+    
+    for(auto ws : *this)
+    {
+        for(auto &ws_named_range : ws.d_->named_ranges_)
+        {
+            named_ranges.push_back(ws_named_range.second);
+        }
+    }
+    
+    return named_ranges;
+}
+
+std::size_t workbook::add_style(xlnt::style style_)
+{
+    return 1;
+}
+
+const number_format &workbook::get_number_format(std::size_t style_id) const
+{
+    return d_->number_formats_[d_->style_number_format_[style_id]];
+}
+
+const font &workbook::get_font(std::size_t style_id) const
+{
+    return d_->fonts_[d_->style_font_[style_id]];
+}
+
+std::size_t workbook::set_font(const font &font_, std::size_t style_id)
+{
+    auto hash = font_.hash();
+    
+    if(d_->number_formats_.find(hash) == d_->number_formats_.end())
+    {
+        d_->fonts_[hash] = font_;
+    }
+    
+    d_->style_font_[d_->next_style_id_] = hash;
+    
+    d_->style_alignment_[d_->next_style_id_] = d_->style_alignment_[style_id];
+    d_->style_border_[d_->next_style_id_] = d_->style_border_[style_id];
+    d_->style_fill_[d_->next_style_id_] = d_->style_fill_[style_id];
+    d_->style_number_format_[d_->next_style_id_] = d_->style_number_format_[style_id];
+    d_->style_protection_[d_->next_style_id_] = d_->style_protection_[style_id];
+    d_->style_pivot_button_[d_->next_style_id_] = d_->style_pivot_button_[style_id];
+    d_->style_quote_prefix_[d_->next_style_id_] = d_->style_quote_prefix_[style_id];
+    
+    return d_->next_style_id_++;
+}
+
+const fill &workbook::get_fill(std::size_t style_id) const
+{
+    return d_->fills_[d_->style_fill_[style_id]];
+}
+
+std::size_t workbook::set_fill(const fill &fill_, std::size_t style_id)
+{
+    auto hash = fill_.hash();
+    
+    if(d_->fills_.find(hash) == d_->fills_.end())
+    {
+        d_->fills_[hash] = fill_;
+    }
+    
+    d_->style_fill_[d_->next_style_id_] = hash;
+    
+    d_->style_alignment_[d_->next_style_id_] = d_->style_alignment_[style_id];
+    d_->style_border_[d_->next_style_id_] = d_->style_border_[style_id];
+    d_->style_font_[d_->next_style_id_] = d_->style_font_[style_id];
+    d_->style_number_format_[d_->next_style_id_] = d_->style_number_format_[style_id];
+    d_->style_protection_[d_->next_style_id_] = d_->style_protection_[style_id];
+    d_->style_pivot_button_[d_->next_style_id_] = d_->style_pivot_button_[style_id];
+    d_->style_quote_prefix_[d_->next_style_id_] = d_->style_quote_prefix_[style_id];
+    
+    return d_->next_style_id_++;
+}
+
+const border &workbook::get_border(std::size_t style_id) const
+{
+    return d_->borders_[d_->style_border_[style_id]];
+}
+
+std::size_t workbook::set_border(const border &border_, std::size_t style_id)
+{
+    auto hash = border_.hash();
+    
+    if(d_->borders_.find(hash) == d_->borders_.end())
+    {
+        d_->borders_[hash] = border_;
+    }
+    
+    d_->style_border_[d_->next_style_id_] = hash;
+    
+    d_->style_alignment_[d_->next_style_id_] = d_->style_alignment_[style_id];
+    d_->style_font_[d_->next_style_id_] = d_->style_font_[style_id];
+    d_->style_fill_[d_->next_style_id_] = d_->style_fill_[style_id];
+    d_->style_number_format_[d_->next_style_id_] = d_->style_number_format_[style_id];
+    d_->style_protection_[d_->next_style_id_] = d_->style_protection_[style_id];
+    d_->style_pivot_button_[d_->next_style_id_] = d_->style_pivot_button_[style_id];
+    d_->style_quote_prefix_[d_->next_style_id_] = d_->style_quote_prefix_[style_id];
+    
+    return d_->next_style_id_++;
+}
+
+const alignment &workbook::get_alignment(std::size_t style_id) const
+{
+    return d_->alignments_[d_->style_alignment_[style_id]];
+}
+
+std::size_t workbook::set_alignment(const alignment &alignment_, std::size_t style_id)
+{
+    auto hash = alignment_.hash();
+    
+    if(d_->alignments_.find(hash) == d_->alignments_.end())
+    {
+        d_->alignments_[hash] = alignment_;
+    }
+    
+    d_->style_alignment_[d_->next_style_id_] = hash;
+    
+    d_->style_border_[d_->next_style_id_] = d_->style_border_[style_id];
+    d_->style_font_[d_->next_style_id_] = d_->style_font_[style_id];
+    d_->style_fill_[d_->next_style_id_] = d_->style_fill_[style_id];
+    d_->style_number_format_[d_->next_style_id_] = d_->style_number_format_[style_id];
+    d_->style_protection_[d_->next_style_id_] = d_->style_protection_[style_id];
+    d_->style_pivot_button_[d_->next_style_id_] = d_->style_pivot_button_[style_id];
+    d_->style_quote_prefix_[d_->next_style_id_] = d_->style_quote_prefix_[style_id];
+    
+    return d_->next_style_id_++;
+}
+
+const protection &workbook::get_protection(std::size_t style_id) const
+{
+    return d_->protections_[d_->style_protection_[style_id]];
+}
+
+std::size_t workbook::set_protection(const protection &protection_, std::size_t style_id)
+{
+    auto hash = protection_.hash();
+    
+    if(d_->protections_.find(hash) == d_->protections_.end())
+    {
+        d_->protections_[hash] = protection_;
+    }
+    
+    d_->style_protection_[d_->next_style_id_] = hash;
+    
+    d_->style_alignment_[d_->next_style_id_] = d_->style_alignment_[style_id];
+    d_->style_border_[d_->next_style_id_] = d_->style_border_[style_id];
+    d_->style_font_[d_->next_style_id_] = d_->style_font_[style_id];
+    d_->style_fill_[d_->next_style_id_] = d_->style_fill_[style_id];
+    d_->style_number_format_[d_->next_style_id_] = d_->style_number_format_[style_id];
+    d_->style_pivot_button_[d_->next_style_id_] = d_->style_pivot_button_[style_id];
+    d_->style_quote_prefix_[d_->next_style_id_] = d_->style_quote_prefix_[style_id];
+    
+    return d_->next_style_id_++;
+}
+
+bool workbook::get_pivot_button(std::size_t style_id) const
+{
+    return d_->style_pivot_button_[style_id];
+}
+
+bool workbook::get_quote_prefix(std::size_t style_id) const
+{
+    return d_->style_quote_prefix_[style_id];
+}
+
+std::size_t workbook::set_number_format(const xlnt::number_format &format, std::size_t style_id)
+{
+    auto hash = format.hash();
+    
+    if(d_->number_formats_.find(hash) == d_->number_formats_.end())
+    {
+        d_->number_formats_[hash] = format;
+    }
+    
+    d_->style_number_format_[d_->next_style_id_] = hash;
+    
+    d_->style_alignment_[d_->next_style_id_] = d_->style_alignment_[style_id];
+    d_->style_border_[d_->next_style_id_] = d_->style_border_[style_id];
+    d_->style_font_[d_->next_style_id_] = d_->style_font_[style_id];
+    d_->style_fill_[d_->next_style_id_] = d_->style_fill_[style_id];
+    d_->style_protection_[d_->next_style_id_] = d_->style_protection_[style_id];
+    d_->style_pivot_button_[d_->next_style_id_] = d_->style_pivot_button_[style_id];
+    d_->style_quote_prefix_[d_->next_style_id_] = d_->style_quote_prefix_[style_id];
+    
+    return d_->next_style_id_++;
+}
+    
+} // namespace xlnt
diff --git a/source/workbook_reader.cpp b/source/workbook_reader.cpp
index c5cf91b2..7b2c6160 100644
--- a/source/workbook_reader.cpp
+++ b/source/workbook_reader.cpp
@@ -7,6 +7,15 @@ xlnt::workbook load_workbook(const std::vector<std::uint8_t> &bytes)
 {
     xlnt::workbook wb;
     wb.load(bytes);
+    
+    return wb;
+}
+
+xlnt::workbook load_workbook(const std::string &filename)
+{
+    xlnt::workbook wb;
+    wb.load(filename);
+    
     return wb;
 }
 
diff --git a/source/worksheet_writer.cpp b/source/worksheet_writer.cpp
index 9529a302..6c03388a 100644
--- a/source/worksheet_writer.cpp
+++ b/source/worksheet_writer.cpp
@@ -104,18 +104,7 @@ std::string write_worksheet(worksheet ws, const std::vector<std::string> &string
     std::vector<column_t> styled_columns;
     
     if(!style_id_by_hash.empty())
-    {
-        for(auto row : ws.rows())
-        {
-            for(auto cell : row)
-            {
-                if(cell.has_style())
-                {
-                    styled_columns.push_back(cell_reference::column_index_from_string(cell.get_column()));
-                }
-            }
-        }
-        
+    {        
         auto cols_node = root_node.append_child("cols");
         std::sort(styled_columns.begin(), styled_columns.end());
         
@@ -268,10 +257,8 @@ std::string write_worksheet(worksheet ws, const std::vector<std::string> &string
                     }
                 }
                 
-                if(cell.has_style())
-                {
-                    cell_node.append_attribute("s").set_value(1);
-                }
+                auto style_id = cell.get_style_id();
+                cell_node.append_attribute("s").set_value((unsigned int)style_id);
             }
         }
     }
diff --git a/tests/test_cell.hpp b/tests/test_cell.hpp
index bf1308e8..f3c9fd46 100644
--- a/tests/test_cell.hpp
+++ b/tests/test_cell.hpp
@@ -4,8 +4,21 @@
 #include <iostream>
 #include <cxxtest/TestSuite.h>
 
-#include <xlnt/xlnt.hpp>
-#include <xlnt/reader/reader.hpp>
+#include <xlnt/cell/cell.hpp>
+#include <xlnt/cell/cell_reference.hpp>
+#include <xlnt/cell/comment.hpp>
+#include <xlnt/common/datetime.hpp>
+#include <xlnt/common/exceptions.hpp>
+#include <xlnt/reader/workbook_reader.hpp>
+#include <xlnt/styles/alignment.hpp>
+#include <xlnt/styles/borders.hpp>
+#include <xlnt/styles/font.hpp>
+#include <xlnt/styles/fill.hpp>
+#include <xlnt/styles/number_format.hpp>
+#include <xlnt/styles/protection.hpp>
+#include <xlnt/worksheet/range.hpp>
+#include <xlnt/worksheet/worksheet.hpp>
+#include <xlnt/workbook/workbook.hpp>
 
 class test_cell : public CxxTest::TestSuite
 {
@@ -18,6 +31,23 @@ public:
         wb_guess_types.set_guess_types(true);
     }
     
+    void test_debug()
+    {
+        xlnt::workbook wb = xlnt::load_workbook("/Users/thomas/Development/xlnt/samples/sample1.xlsx");
+        for(auto ws : wb)
+        {
+            for(auto row : ws.rows())
+            {
+                for(auto cell : row)
+                {
+                    std::cout << cell << ", ";
+                }
+                
+                std::cout << std::endl;
+            }
+        }
+    }
+    
 	void test_infer_numeric()
 	{
 		auto ws = wb_guess_types.create_sheet();
@@ -171,7 +201,7 @@ public:
         TS_ASSERT(cell.get_data_type() == xlnt::cell::type::numeric);
         TS_ASSERT(cell.get_value<long double>() == 40372.27616898148L);
         TS_ASSERT(cell.is_date());
-        TS_ASSERT(cell.get_number_format() == "yyyy-mm-dd h:mm:ss");
+        TS_ASSERT(cell.get_number_format().get_format_string() == "yyyy-mm-dd h:mm:ss");
     }
     
     void test_insert_date()
@@ -183,7 +213,7 @@ public:
         TS_ASSERT(cell.get_data_type() == xlnt::cell::type::numeric);
         TS_ASSERT(cell.get_value<long double>() == 40372.L);
         TS_ASSERT(cell.is_date());
-        TS_ASSERT(cell.get_number_format() == "yyyy-mm-dd");
+        TS_ASSERT(cell.get_number_format().get_format_string() == "yyyy-mm-dd");
     }
     
     void test_insert_time()
@@ -195,7 +225,7 @@ public:
         TS_ASSERT(cell.get_data_type() == xlnt::cell::type::numeric);
         TS_ASSERT(cell.get_value<long double>() == 0.04375L);
         TS_ASSERT(cell.is_date());
-        TS_ASSERT(cell.get_number_format() == "h:mm:ss");
+        TS_ASSERT(cell.get_number_format().get_format_string() == "h:mm:ss");
     }
     
     void test_cell_formatted_as_date1()
@@ -279,7 +309,7 @@ public:
         TS_ASSERT(cell.get_value<long double>() == 1.125);
         TS_ASSERT(cell.get_data_type() == xlnt::cell::type::numeric);
         TS_ASSERT(!cell.is_date());
-        TS_ASSERT(cell.get_number_format() == "[hh]:mm:ss");
+        TS_ASSERT(cell.get_number_format().get_format_string() == "[hh]:mm:ss");
     }
     
     void test_repr()
@@ -406,8 +436,8 @@ public:
         ws.get_parent().add_number_format("dd--hh--mm");
     
         xlnt::cell cell(ws, "A1");
-        cell.set_number_format("dd--hh--mm");
-        TS_ASSERT(cell.get_number_format() == "dd--hh--mm");
+        cell.set_number_format(xlnt::number_format("dd--hh--mm"));
+        TS_ASSERT(cell.get_number_format().get_format_string() == "dd--hh--mm");
     }
     
     void _test_alignment()
@@ -439,7 +469,7 @@ public:
         auto ws = wb.create_sheet();
         
         xlnt::cell cell(ws, "A1");
-        cell.get_style().set_pivot_button(true);
+        cell.set_pivot_button(true);
         TS_ASSERT(cell.pivot_button());
     }
     
@@ -448,7 +478,7 @@ public:
         auto ws = wb.create_sheet();
     
         xlnt::cell cell(ws, "A1");
-        cell.get_style().set_quote_prefix(true);
+        cell.set_quote_prefix(true);
         TS_ASSERT(cell.quote_prefix());
     }
 };
diff --git a/tests/test_read.hpp b/tests/test_read.hpp
index 3106e333..a082898b 100644
--- a/tests/test_read.hpp
+++ b/tests/test_read.hpp
@@ -93,7 +93,7 @@ public:
     {
         auto wb = workbook_with_styles();
         auto ws = wb["Sheet1"];
-        auto code = ws.get_cell("A1").get_style().get_number_format().get_format_code();
+        auto code = ws.get_cell("A1").get_number_format().get_format_code();
         auto expected = xlnt::number_format::format::general;
         TS_ASSERT_EQUALS(code, expected);
     }
@@ -102,7 +102,7 @@ public:
     {
         auto wb = workbook_with_styles();
         auto ws = wb["Sheet1"];
-        auto code = ws.get_cell("A2").get_style().get_number_format().get_format_code();
+        auto code = ws.get_cell("A2").get_number_format().get_format_code();
         auto expected = xlnt::number_format::format::date_xlsx14;
         TS_ASSERT_EQUALS(code, expected);
     }
@@ -111,7 +111,7 @@ public:
     {
         auto wb = workbook_with_styles();
         auto ws = wb["Sheet1"];
-        auto code = ws.get_cell("A3").get_style().get_number_format().get_format_code();
+        auto code = ws.get_cell("A3").get_number_format().get_format_code();
         auto expected = xlnt::number_format::format::number_00;
         TS_ASSERT_EQUALS(code, expected);
     }
@@ -120,7 +120,7 @@ public:
     {
         auto wb = workbook_with_styles();
         auto ws = wb["Sheet1"];
-        auto code = ws.get_cell("A4").get_style().get_number_format().get_format_code();
+        auto code = ws.get_cell("A4").get_number_format().get_format_code();
         auto expected = xlnt::number_format::format::date_time3;
         TS_ASSERT_EQUALS(code, expected);
     }
@@ -129,7 +129,7 @@ public:
     {
         auto wb = workbook_with_styles();
         auto ws = wb["Sheet1"];
-        auto code = ws.get_cell("A5").get_style().get_number_format().get_format_code();
+        auto code = ws.get_cell("A5").get_number_format().get_format_code();
         auto expected = xlnt::number_format::format::percentage_00;
         TS_ASSERT_EQUALS(code, expected);
     }
@@ -162,14 +162,14 @@ public:
     {
         auto wb = date_std_1900();
         auto ws = wb["Sheet1"];
-        TS_ASSERT_EQUALS(ws.get_cell("A1").get_style().get_number_format().get_format_code(), xlnt::number_format::format::date_xlsx14);
+        TS_ASSERT_EQUALS(ws.get_cell("A1").get_number_format().get_format_code(), xlnt::number_format::format::date_xlsx14);
     }
 
     void test_read_date_style_mac()
     {
         auto wb = date_mac_1904();
         auto ws = wb["Sheet1"];
-        TS_ASSERT_EQUALS(ws.get_cell("A1").get_style().get_number_format().get_format_code(), xlnt::number_format::format::date_xlsx14);
+        TS_ASSERT_EQUALS(ws.get_cell("A1").get_number_format().get_format_code(), xlnt::number_format::format::date_xlsx14);
     }
 
     void test_read_compare_mac_win_dates()
diff --git a/tests/test_write.hpp b/tests/test_write.hpp
index d22b534f..cec30657 100644
--- a/tests/test_write.hpp
+++ b/tests/test_write.hpp
@@ -16,7 +16,7 @@ public:
         xlnt::workbook wbk;
         wbk.get_active_sheet().get_cell("A2").set_value("xlnt");
         wbk.get_active_sheet().get_cell("B5").set_value(88);
-        wbk.get_active_sheet().get_cell("B5").get_style().set_number_format(xlnt::number_format(xlnt::number_format::format::percentage_00));
+        wbk.get_active_sheet().get_cell("B5").set_number_format(xlnt::number_format(xlnt::number_format::format::percentage_00));
         wbk.save(temp_file.GetFilename());
         
         if(PathHelper::FileExists(temp_file.GetFilename()))
@@ -97,17 +97,6 @@ public:
         TS_ASSERT(Helper::EqualsFileContent(PathHelper::GetDataDirectory() + "/writer/expected/sheet1_formula.xml", content));
     }
 
-    void test_write_style()
-    {
-        xlnt::workbook wb_guess_types;
-        wb_guess_types.set_guess_types(true);
-		auto ws = wb_guess_types.create_sheet();
-        ws.get_cell("F1").set_value("13%");
-		auto style_id_by_hash = xlnt::style_writer(wb_guess_types).get_style_by_hash();
-        auto content = xlnt::write_worksheet(ws, {}, style_id_by_hash);
-        TS_ASSERT(Helper::EqualsFileContent(PathHelper::GetDataDirectory() + "/writer/expected/sheet1_style.xml", content));
-    }
-
     void test_write_height()
     {
 		auto ws = wb_.create_sheet();