diff --git a/ClosedXML/Excel/Cells/XLCell.cs b/ClosedXML/Excel/Cells/XLCell.cs
index f9f30dd..dab1b88 100644
--- a/ClosedXML/Excel/Cells/XLCell.cs
+++ b/ClosedXML/Excel/Cells/XLCell.cs
@@ -92,7 +92,7 @@
         }
 
         public XLCell(XLWorksheet worksheet, XLAddress address, IXLStyle style)
-            : this(worksheet, address, style.Value)
+            : this(worksheet, address, (style as XLStyle).Value)
         {
         }
 
diff --git a/ClosedXML/Excel/Columns/XLColumn.cs b/ClosedXML/Excel/Columns/XLColumn.cs
index 607f181..791c595 100644
--- a/ClosedXML/Excel/Columns/XLColumn.cs
+++ b/ClosedXML/Excel/Columns/XLColumn.cs
@@ -25,7 +25,7 @@
                                    new XLAddress(xlColumnParameters.Worksheet, XLHelper.MaxRowNumber, column, false,
                                                  false)),
                 xlColumnParameters.IsReference ? xlColumnParameters.Worksheet.Internals.ColumnsCollection[column].StyleValue
-                                               : xlColumnParameters.DefaultStyle.Value)
+                                               : (xlColumnParameters.DefaultStyle as XLStyle).Value)
         {
             SetColumnNumber(column);
 
@@ -267,12 +267,12 @@
                     && !autoFilterRows.Contains(t.AutoFilter.Range.FirstRow().RowNumber()))
                 .Select(t => t.AutoFilter.Range.FirstRow().RowNumber()));
 
-            IXLStyle cellStyle = null;
-            foreach (XLCell c in Column(startRow, endRow).CellsUsed())
+            XLStyle cellStyle = null;
+            foreach (var c in Column(startRow, endRow).CellsUsed().Cast<XLCell>())
             {
                 if (c.IsMerged()) continue;
                 if (cellStyle == null || cellStyle.Value != c.StyleValue)
-                    cellStyle = c.Style;
+                    cellStyle = c.Style as XLStyle;
 
                 Double thisWidthMax = 0;
                 Int32 textRotation = cellStyle.Alignment.TextRotation;
diff --git a/ClosedXML/Excel/ConditionalFormats/Save/XLCFCellIsConverter.cs b/ClosedXML/Excel/ConditionalFormats/Save/XLCFCellIsConverter.cs
index 72c297a..2a3bf8e 100644
--- a/ClosedXML/Excel/ConditionalFormats/Save/XLCFCellIsConverter.cs
+++ b/ClosedXML/Excel/ConditionalFormats/Save/XLCFCellIsConverter.cs
@@ -10,8 +10,8 @@
             String val = GetQuoted(cf.Values[1]);
 
             var conditionalFormattingRule = XLCFBaseConverter.Convert(cf, priority);
-            var cfStyle = cf.Style.Value;
-            if (!cfStyle.Equals(XLWorkbook.DefaultStyle.Value))
+            var cfStyle = (cf.Style as XLStyle).Value;
+            if (!cfStyle.Equals(XLWorkbook.DefaultStyleValue))
                 conditionalFormattingRule.FormatId = (UInt32)context.DifferentialFormats[cfStyle.Key];
 
             conditionalFormattingRule.Operator = cf.Operator.ToOpenXml();
diff --git a/ClosedXML/Excel/ConditionalFormats/Save/XLCFContainsConverter.cs b/ClosedXML/Excel/ConditionalFormats/Save/XLCFContainsConverter.cs
index bb25709..435e690 100644
--- a/ClosedXML/Excel/ConditionalFormats/Save/XLCFContainsConverter.cs
+++ b/ClosedXML/Excel/ConditionalFormats/Save/XLCFContainsConverter.cs
@@ -9,8 +9,8 @@
         {
             String val = cf.Values[1].Value;
             var conditionalFormattingRule = XLCFBaseConverter.Convert(cf, priority);
-            var cfStyle = cf.Style.Value;
-            if (!cfStyle.Equals(XLWorkbook.DefaultStyle.Value))
+            var cfStyle = (cf.Style as XLStyle).Value;
+            if (!cfStyle.Equals(XLWorkbook.DefaultStyleValue))
                 conditionalFormattingRule.FormatId = (UInt32)context.DifferentialFormats[cfStyle.Key];
 
             conditionalFormattingRule.Operator = ConditionalFormattingOperatorValues.ContainsText;
diff --git a/ClosedXML/Excel/ConditionalFormats/Save/XLCFDatesOccuringConverter.cs b/ClosedXML/Excel/ConditionalFormats/Save/XLCFDatesOccuringConverter.cs
index 82bcf6d..a1375b7 100644
--- a/ClosedXML/Excel/ConditionalFormats/Save/XLCFDatesOccuringConverter.cs
+++ b/ClosedXML/Excel/ConditionalFormats/Save/XLCFDatesOccuringConverter.cs
@@ -23,8 +23,8 @@
         public ConditionalFormattingRule Convert(IXLConditionalFormat cf, int priority, XLWorkbook.SaveContext context)
         {
             var conditionalFormattingRule = XLCFBaseConverter.Convert(cf, priority);
-            var cfStyle = cf.Style.Value;
-            if (!cfStyle.Equals(XLWorkbook.DefaultStyle))
+            var cfStyle = (cf.Style as XLStyle).Value;
+            if (!cfStyle.Equals(XLWorkbook.DefaultStyleValue))
                 conditionalFormattingRule.FormatId = (UInt32)context.DifferentialFormats[cfStyle.Key];
 
             conditionalFormattingRule.TimePeriod = cf.TimePeriod.ToOpenXml();
diff --git a/ClosedXML/Excel/ConditionalFormats/Save/XLCFEndsWithConverter.cs b/ClosedXML/Excel/ConditionalFormats/Save/XLCFEndsWithConverter.cs
index fa0f6d5..a65194a 100644
--- a/ClosedXML/Excel/ConditionalFormats/Save/XLCFEndsWithConverter.cs
+++ b/ClosedXML/Excel/ConditionalFormats/Save/XLCFEndsWithConverter.cs
@@ -9,8 +9,8 @@
         {
             String val = cf.Values[1].Value;
             var conditionalFormattingRule = XLCFBaseConverter.Convert(cf, priority);
-            var cfStyle = cf.Style.Value;
-            if (!cfStyle.Equals(XLWorkbook.DefaultStyle))
+            var cfStyle = (cf.Style as XLStyle).Value;
+            if (!cfStyle.Equals(XLWorkbook.DefaultStyleValue))
                 conditionalFormattingRule.FormatId = (UInt32)context.DifferentialFormats[cfStyle.Key];
 
             conditionalFormattingRule.Operator = ConditionalFormattingOperatorValues.EndsWith;
diff --git a/ClosedXML/Excel/ConditionalFormats/Save/XLCFIsBlankConverter.cs b/ClosedXML/Excel/ConditionalFormats/Save/XLCFIsBlankConverter.cs
index 6d282a9..07eccac 100644
--- a/ClosedXML/Excel/ConditionalFormats/Save/XLCFIsBlankConverter.cs
+++ b/ClosedXML/Excel/ConditionalFormats/Save/XLCFIsBlankConverter.cs
@@ -8,8 +8,8 @@
         public ConditionalFormattingRule Convert(IXLConditionalFormat cf, int priority, XLWorkbook.SaveContext context)
         {
             var conditionalFormattingRule = XLCFBaseConverter.Convert(cf, priority);
-            var cfStyle = cf.Style.Value;
-            if (!cfStyle.Equals(XLWorkbook.DefaultStyle.Value))
+            var cfStyle = (cf.Style as XLStyle).Value;
+            if (!cfStyle.Equals(XLWorkbook.DefaultStyleValue))
                 conditionalFormattingRule.FormatId = (UInt32)context.DifferentialFormats[cfStyle.Key];
 
             var formula = new Formula { Text = "LEN(TRIM(" + cf.Range.RangeAddress.FirstAddress.ToStringRelative(false) + "))=0" };
diff --git a/ClosedXML/Excel/ConditionalFormats/Save/XLCFIsErrorConverter.cs b/ClosedXML/Excel/ConditionalFormats/Save/XLCFIsErrorConverter.cs
index bf2170f..1cfb4fe 100644
--- a/ClosedXML/Excel/ConditionalFormats/Save/XLCFIsErrorConverter.cs
+++ b/ClosedXML/Excel/ConditionalFormats/Save/XLCFIsErrorConverter.cs
@@ -8,8 +8,8 @@
         public ConditionalFormattingRule Convert(IXLConditionalFormat cf, int priority, XLWorkbook.SaveContext context)
         {
             var conditionalFormattingRule = XLCFBaseConverter.Convert(cf, priority);
-            var cfStyle = cf.Style.Value;
-            if (!cfStyle.Equals(XLWorkbook.DefaultStyle.Value))
+            var cfStyle = (cf.Style as XLStyle).Value;
+            if (!cfStyle.Equals(XLWorkbook.DefaultStyleValue))
                 conditionalFormattingRule.FormatId = (UInt32)context.DifferentialFormats[cfStyle.Key];
 
             var formula = new Formula { Text = "ISERROR(" + cf.Range.RangeAddress.FirstAddress.ToStringRelative(false) + ")" };
diff --git a/ClosedXML/Excel/ConditionalFormats/Save/XLCFNotBlankConverter.cs b/ClosedXML/Excel/ConditionalFormats/Save/XLCFNotBlankConverter.cs
index 532777a..4e36698 100644
--- a/ClosedXML/Excel/ConditionalFormats/Save/XLCFNotBlankConverter.cs
+++ b/ClosedXML/Excel/ConditionalFormats/Save/XLCFNotBlankConverter.cs
@@ -8,8 +8,8 @@
         public ConditionalFormattingRule Convert(IXLConditionalFormat cf, int priority, XLWorkbook.SaveContext context)
         {
             var conditionalFormattingRule = XLCFBaseConverter.Convert(cf, priority);
-            var cfStyle = cf.Style.Value;
-            if (!cfStyle.Equals(XLWorkbook.DefaultStyle.Value))
+            var cfStyle = (cf.Style as XLStyle).Value;
+            if (!cfStyle.Equals(XLWorkbook.DefaultStyleValue))
                 conditionalFormattingRule.FormatId = (UInt32)context.DifferentialFormats[cfStyle.Key];
 
             var formula = new Formula { Text = "LEN(TRIM(" + cf.Range.RangeAddress.FirstAddress.ToStringRelative(false) + "))>0" };
diff --git a/ClosedXML/Excel/ConditionalFormats/Save/XLCFNotContainsConverter.cs b/ClosedXML/Excel/ConditionalFormats/Save/XLCFNotContainsConverter.cs
index 0c3bf31..8849d74 100644
--- a/ClosedXML/Excel/ConditionalFormats/Save/XLCFNotContainsConverter.cs
+++ b/ClosedXML/Excel/ConditionalFormats/Save/XLCFNotContainsConverter.cs
@@ -9,8 +9,8 @@
         {
             String val = cf.Values[1].Value;
             var conditionalFormattingRule = XLCFBaseConverter.Convert(cf, priority);
-            var cfStyle = cf.Style.Value;
-            if (!cfStyle.Equals(XLWorkbook.DefaultStyle))
+            var cfStyle = (cf.Style as XLStyle).Value;
+            if (!cfStyle.Equals(XLWorkbook.DefaultStyleValue))
                 conditionalFormattingRule.FormatId = (UInt32)context.DifferentialFormats[cfStyle.Key];
 
             conditionalFormattingRule.Operator = ConditionalFormattingOperatorValues.NotContains;
diff --git a/ClosedXML/Excel/ConditionalFormats/Save/XLCFNotErrorConverter.cs b/ClosedXML/Excel/ConditionalFormats/Save/XLCFNotErrorConverter.cs
index 7798815..51b794b 100644
--- a/ClosedXML/Excel/ConditionalFormats/Save/XLCFNotErrorConverter.cs
+++ b/ClosedXML/Excel/ConditionalFormats/Save/XLCFNotErrorConverter.cs
@@ -8,8 +8,8 @@
         public ConditionalFormattingRule Convert(IXLConditionalFormat cf, int priority, XLWorkbook.SaveContext context)
         {
             var conditionalFormattingRule = XLCFBaseConverter.Convert(cf, priority);
-            var cfStyle = cf.Style.Value;
-            if (!cfStyle.Equals(XLWorkbook.DefaultStyle.Value))
+            var cfStyle = (cf.Style as XLStyle).Value;
+            if (!cfStyle.Equals(XLWorkbook.DefaultStyleValue))
                 conditionalFormattingRule.FormatId = (UInt32)context.DifferentialFormats[cfStyle.Key];
 
             var formula = new Formula { Text = "NOT(ISERROR(" + cf.Range.RangeAddress.FirstAddress.ToStringRelative(false) + "))" };
diff --git a/ClosedXML/Excel/ConditionalFormats/Save/XLCFStartsWithConverter.cs b/ClosedXML/Excel/ConditionalFormats/Save/XLCFStartsWithConverter.cs
index 1ede504..5f1721e 100644
--- a/ClosedXML/Excel/ConditionalFormats/Save/XLCFStartsWithConverter.cs
+++ b/ClosedXML/Excel/ConditionalFormats/Save/XLCFStartsWithConverter.cs
@@ -9,8 +9,8 @@
         {
             String val = cf.Values[1].Value;
             var conditionalFormattingRule = XLCFBaseConverter.Convert(cf, priority);
-            var cfStyle = cf.Style.Value;
-            if (!cfStyle.Equals(XLWorkbook.DefaultStyle.Value))
+            var cfStyle = (cf.Style as XLStyle).Value;
+            if (!cfStyle.Equals(XLWorkbook.DefaultStyleValue))
                 conditionalFormattingRule.FormatId = (UInt32)context.DifferentialFormats[cfStyle.Key];
 
             conditionalFormattingRule.Operator = ConditionalFormattingOperatorValues.BeginsWith;
diff --git a/ClosedXML/Excel/ConditionalFormats/Save/XLCFTopConverter.cs b/ClosedXML/Excel/ConditionalFormats/Save/XLCFTopConverter.cs
index 194f183..cc4accc 100644
--- a/ClosedXML/Excel/ConditionalFormats/Save/XLCFTopConverter.cs
+++ b/ClosedXML/Excel/ConditionalFormats/Save/XLCFTopConverter.cs
@@ -9,8 +9,8 @@
         {
             UInt32 val = UInt32.Parse(cf.Values[1].Value);
             var conditionalFormattingRule = XLCFBaseConverter.Convert(cf, priority);
-            var cfStyle = cf.Style.Value;
-            if (!cfStyle.Equals(XLWorkbook.DefaultStyle.Value))
+            var cfStyle = (cf.Style as XLStyle).Value;
+            if (!cfStyle.Equals(XLWorkbook.DefaultStyleValue))
                 conditionalFormattingRule.FormatId = (UInt32)context.DifferentialFormats[cfStyle.Key];
 
             conditionalFormattingRule.Percent = cf.Percent;
diff --git a/ClosedXML/Excel/ConditionalFormats/Save/XLCFUniqueConverter.cs b/ClosedXML/Excel/ConditionalFormats/Save/XLCFUniqueConverter.cs
index 673fae8..7c5035e 100644
--- a/ClosedXML/Excel/ConditionalFormats/Save/XLCFUniqueConverter.cs
+++ b/ClosedXML/Excel/ConditionalFormats/Save/XLCFUniqueConverter.cs
@@ -8,8 +8,8 @@
         public ConditionalFormattingRule Convert(IXLConditionalFormat cf, int priority, XLWorkbook.SaveContext context)
         {
             var conditionalFormattingRule = XLCFBaseConverter.Convert(cf, priority);
-            var cfStyle = cf.Style.Value;
-            if (!cfStyle.Equals(XLWorkbook.DefaultStyle.Value))
+            var cfStyle = (cf.Style as XLStyle).Value;
+            if (!cfStyle.Equals(XLWorkbook.DefaultStyleValue))
                 conditionalFormattingRule.FormatId = (UInt32)context.DifferentialFormats[cfStyle.Key];
 
             return conditionalFormattingRule;
diff --git a/ClosedXML/Excel/ConditionalFormats/XLConditionalFormat.cs b/ClosedXML/Excel/ConditionalFormats/XLConditionalFormat.cs
index 0140281..f348160 100644
--- a/ClosedXML/Excel/ConditionalFormats/XLConditionalFormat.cs
+++ b/ClosedXML/Excel/ConditionalFormats/XLConditionalFormat.cs
@@ -60,7 +60,7 @@
             public int GetHashCode(IXLConditionalFormat obj)
             {
                 var xx = (XLConditionalFormat)obj;
-                var xStyle = obj.Style.Value;
+                var xStyle = (obj.Style as XLStyle).Value;
                 var xValues = xx.Values.Values.Where(v => !v.IsFormula).Select(v => v.Value)
                     .Union(xx.Values.Values.Where(v => v.IsFormula).Select(f => ((XLCell)obj.Range.FirstCell()).GetFormulaR1C1(f.Value)));
 
diff --git a/ClosedXML/Excel/Ranges/XLRange.cs b/ClosedXML/Excel/Ranges/XLRange.cs
index 7a20194..fbee6dd 100644
--- a/ClosedXML/Excel/Ranges/XLRange.cs
+++ b/ClosedXML/Excel/Ranges/XLRange.cs
@@ -9,7 +9,7 @@
         #region Constructor
 
         public XLRange(XLRangeParameters xlRangeParameters)
-            : base(xlRangeParameters.RangeAddress, xlRangeParameters.DefaultStyle.Value)
+            : base(xlRangeParameters.RangeAddress, (xlRangeParameters.DefaultStyle as XLStyle).Value)
         {
             RangeParameters = new XLRangeParameters(xlRangeParameters.RangeAddress, xlRangeParameters.DefaultStyle);
 
@@ -245,7 +245,7 @@
 
             foreach (IXLCell c in Range(1, 1, columnCount, rowCount).Cells())
             {
-                var border = c.Style.Value.Border;
+                var border = (c.Style as XLStyle).Value.Border;
                 c.Style.Border.TopBorder = border.LeftBorder;
                 c.Style.Border.TopBorderColor = border.LeftBorderColor;
                 c.Style.Border.LeftBorder = border.TopBorder;
diff --git a/ClosedXML/Excel/Ranges/XLRangeColumn.cs b/ClosedXML/Excel/Ranges/XLRangeColumn.cs
index a642b56..c027859 100644
--- a/ClosedXML/Excel/Ranges/XLRangeColumn.cs
+++ b/ClosedXML/Excel/Ranges/XLRangeColumn.cs
@@ -8,7 +8,7 @@
         #region Constructor
 
         public XLRangeColumn(XLRangeParameters rangeParameters, bool quickLoad)
-            : base(rangeParameters.RangeAddress, rangeParameters.DefaultStyle.Value)
+            : base(rangeParameters.RangeAddress, (rangeParameters.DefaultStyle as XLStyle).Value)
         {
             if (quickLoad) return;
 
diff --git a/ClosedXML/Excel/Ranges/XLRangeColumns.cs b/ClosedXML/Excel/Ranges/XLRangeColumns.cs
index ede54ff..170cd3f 100644
--- a/ClosedXML/Excel/Ranges/XLRangeColumns.cs
+++ b/ClosedXML/Excel/Ranges/XLRangeColumns.cs
@@ -10,7 +10,7 @@
     {
         private readonly List<XLRangeColumn> _ranges = new List<XLRangeColumn>();
 
-        public XLRangeColumns() : base(XLWorkbook.DefaultStyle.Value)
+        public XLRangeColumns() : base(XLWorkbook.DefaultStyleValue)
         {
         }
 
diff --git a/ClosedXML/Excel/Ranges/XLRangeRow.cs b/ClosedXML/Excel/Ranges/XLRangeRow.cs
index ec245c5..bd0034c 100644
--- a/ClosedXML/Excel/Ranges/XLRangeRow.cs
+++ b/ClosedXML/Excel/Ranges/XLRangeRow.cs
@@ -8,7 +8,7 @@
         #region Constructor
 
         public XLRangeRow(XLRangeParameters rangeParameters, bool quickLoad)
-            : base(rangeParameters.RangeAddress, rangeParameters.DefaultStyle.Value)
+            : base(rangeParameters.RangeAddress, (rangeParameters.DefaultStyle as XLStyle).Value)
         {
             RangeParameters = rangeParameters;
             if (quickLoad) return;
diff --git a/ClosedXML/Excel/Ranges/XLRanges.cs b/ClosedXML/Excel/Ranges/XLRanges.cs
index a57186c..b97fc4b 100644
--- a/ClosedXML/Excel/Ranges/XLRanges.cs
+++ b/ClosedXML/Excel/Ranges/XLRanges.cs
@@ -10,7 +10,7 @@
     {
         private readonly List<XLRange> _ranges = new List<XLRange>();
 
-        public XLRanges() : base(XLWorkbook.DefaultStyle.Value)
+        public XLRanges() : base(XLWorkbook.DefaultStyleValue)
         {
         }
 
diff --git a/ClosedXML/Excel/Rows/XLRow.cs b/ClosedXML/Excel/Rows/XLRow.cs
index b4076ca..e52827d 100644
--- a/ClosedXML/Excel/Rows/XLRow.cs
+++ b/ClosedXML/Excel/Rows/XLRow.cs
@@ -23,7 +23,7 @@
                                       new XLAddress(xlRowParameters.Worksheet, row, XLHelper.MaxColumnNumber, false,
                                                     false)),
                   xlRowParameters.IsReference ? xlRowParameters.Worksheet.Internals.RowsCollection[row].StyleValue
-                                              : xlRowParameters.DefaultStyle.Value
+                                              : (xlRowParameters.DefaultStyle as XLStyle).Value
                   )
         {
             SetRowNumber(row);
diff --git a/ClosedXML/Excel/Rows/XLRows.cs b/ClosedXML/Excel/Rows/XLRows.cs
index c7a9321..8494f8f 100644
--- a/ClosedXML/Excel/Rows/XLRows.cs
+++ b/ClosedXML/Excel/Rows/XLRows.cs
@@ -11,7 +11,7 @@
         private readonly List<XLRow> _rows = new List<XLRow>();
         private readonly XLWorksheet _worksheet;
 
-        public XLRows(XLWorksheet worksheet) : base(XLWorkbook.DefaultStyle.Value)
+        public XLRows(XLWorksheet worksheet) : base(XLWorkbook.DefaultStyleValue)
         {
             _worksheet = worksheet;
         }
diff --git a/ClosedXML/Excel/Style/IXLStyle.cs b/ClosedXML/Excel/Style/IXLStyle.cs
index d90eeab..259f568 100644
--- a/ClosedXML/Excel/Style/IXLStyle.cs
+++ b/ClosedXML/Excel/Style/IXLStyle.cs
@@ -17,7 +17,5 @@
         IXLNumberFormat DateFormat { get; }
 
         IXLProtection Protection { get; set; }
-
-        XLStyleValue Value { get; }
     }
 }
diff --git a/ClosedXML/Excel/Style/XLBorderKey.cs b/ClosedXML/Excel/Style/XLBorderKey.cs
index b1fc5eb..0251dfa 100644
--- a/ClosedXML/Excel/Style/XLBorderKey.cs
+++ b/ClosedXML/Excel/Style/XLBorderKey.cs
@@ -2,7 +2,7 @@
 
 namespace ClosedXML.Excel
 {
-    public struct XLBorderKey : IEquatable<XLBorderKey>
+    internal struct XLBorderKey : IEquatable<XLBorderKey>
     {
         public XLBorderStyleValues LeftBorder { get; set; }
 
diff --git a/ClosedXML/Excel/Style/XLBorderValue.cs b/ClosedXML/Excel/Style/XLBorderValue.cs
index 4cb4e01..7c1f8da 100644
--- a/ClosedXML/Excel/Style/XLBorderValue.cs
+++ b/ClosedXML/Excel/Style/XLBorderValue.cs
@@ -2,7 +2,7 @@
 
 namespace ClosedXML.Excel
 {
-    public class XLBorderValue
+    internal class XLBorderValue
     {
         private static readonly XLBorderRepository Repository = new XLBorderRepository(key => new XLBorderValue(key));
 
diff --git a/ClosedXML/Excel/Style/XLColorKey.cs b/ClosedXML/Excel/Style/XLColorKey.cs
index a195739..2484ecf 100644
--- a/ClosedXML/Excel/Style/XLColorKey.cs
+++ b/ClosedXML/Excel/Style/XLColorKey.cs
@@ -2,7 +2,7 @@
 
 namespace ClosedXML.Excel
 {
-    public struct XLColorKey : IEquatable<XLColorKey>
+    internal struct XLColorKey : IEquatable<XLColorKey>
     {
         public XLColorType ColorType { get; set; }
 
diff --git a/ClosedXML/Excel/Style/XLFillKey.cs b/ClosedXML/Excel/Style/XLFillKey.cs
index bb7c930..c2f2495 100644
--- a/ClosedXML/Excel/Style/XLFillKey.cs
+++ b/ClosedXML/Excel/Style/XLFillKey.cs
@@ -2,7 +2,7 @@
 
 namespace ClosedXML.Excel
 {
-    public struct XLFillKey : IEquatable<XLFillKey>
+    internal struct XLFillKey : IEquatable<XLFillKey>
     {
         public XLColorKey BackgroundColor { get; set; }
 
diff --git a/ClosedXML/Excel/Style/XLFillValue.cs b/ClosedXML/Excel/Style/XLFillValue.cs
index 230a278..d12d8fd 100644
--- a/ClosedXML/Excel/Style/XLFillValue.cs
+++ b/ClosedXML/Excel/Style/XLFillValue.cs
@@ -2,7 +2,7 @@
 
 namespace ClosedXML.Excel
 {
-    public sealed class XLFillValue
+    internal sealed class XLFillValue
     {
         private static readonly XLFillRepository Repository = new XLFillRepository(key => new XLFillValue(key));
 
diff --git a/ClosedXML/Excel/Style/XLFontKey.cs b/ClosedXML/Excel/Style/XLFontKey.cs
index e1b93ce..37ee4a0 100644
--- a/ClosedXML/Excel/Style/XLFontKey.cs
+++ b/ClosedXML/Excel/Style/XLFontKey.cs
@@ -2,7 +2,7 @@
 
 namespace ClosedXML.Excel
 {
-    public struct XLFontKey : IEquatable<XLFontKey>
+    internal struct XLFontKey : IEquatable<XLFontKey>
     {
         public bool Bold { get; set; }
 
diff --git a/ClosedXML/Excel/Style/XLFontValue.cs b/ClosedXML/Excel/Style/XLFontValue.cs
index 910633c..088ca07 100644
--- a/ClosedXML/Excel/Style/XLFontValue.cs
+++ b/ClosedXML/Excel/Style/XLFontValue.cs
@@ -3,7 +3,7 @@
 
 namespace ClosedXML.Excel
 {
-    public sealed class XLFontValue
+    internal sealed class XLFontValue
     {
         private static readonly XLFontRepository Repository = new XLFontRepository(key => new XLFontValue(key));
 
diff --git a/ClosedXML/Excel/Style/XLNumberFormatKey.cs b/ClosedXML/Excel/Style/XLNumberFormatKey.cs
index 4d2e412..7a14dc5 100644
--- a/ClosedXML/Excel/Style/XLNumberFormatKey.cs
+++ b/ClosedXML/Excel/Style/XLNumberFormatKey.cs
@@ -2,7 +2,7 @@
 
 namespace ClosedXML.Excel
 {
-    public struct XLNumberFormatKey : IEquatable<XLNumberFormatKey>
+    internal struct XLNumberFormatKey : IEquatable<XLNumberFormatKey>
     {
         public int NumberFormatId { get; set; }
 
diff --git a/ClosedXML/Excel/Style/XLNumberFormatValue.cs b/ClosedXML/Excel/Style/XLNumberFormatValue.cs
index 84a9635..dab2ee1 100644
--- a/ClosedXML/Excel/Style/XLNumberFormatValue.cs
+++ b/ClosedXML/Excel/Style/XLNumberFormatValue.cs
@@ -2,7 +2,7 @@
 
 namespace ClosedXML.Excel
 {
-    public sealed class XLNumberFormatValue
+    internal sealed class XLNumberFormatValue
     {
         private static readonly XLNumberFormatRepository Repository = new XLNumberFormatRepository(key => new XLNumberFormatValue(key));
 
diff --git a/ClosedXML/Excel/Style/XLProtectionKey.cs b/ClosedXML/Excel/Style/XLProtectionKey.cs
index 94637d5..ba4f013 100644
--- a/ClosedXML/Excel/Style/XLProtectionKey.cs
+++ b/ClosedXML/Excel/Style/XLProtectionKey.cs
@@ -2,7 +2,7 @@
 
 namespace ClosedXML.Excel
 {
-    public struct XLProtectionKey : IEquatable<XLProtectionKey>
+    internal struct XLProtectionKey : IEquatable<XLProtectionKey>
     {
         public bool Locked { get; set; }
 
diff --git a/ClosedXML/Excel/Style/XLProtectionValue.cs b/ClosedXML/Excel/Style/XLProtectionValue.cs
index 6d97093..c5520e9 100644
--- a/ClosedXML/Excel/Style/XLProtectionValue.cs
+++ b/ClosedXML/Excel/Style/XLProtectionValue.cs
@@ -2,7 +2,7 @@
 
 namespace ClosedXML.Excel
 {
-    public sealed class XLProtectionValue
+    internal sealed class XLProtectionValue
     {
         private static readonly XLProtectionRepository Repository = new XLProtectionRepository(key => new XLProtectionValue(key));
 
diff --git a/ClosedXML/Excel/Style/XLStyle.cs b/ClosedXML/Excel/Style/XLStyle.cs
index 9d3540b..95e63f2 100644
--- a/ClosedXML/Excel/Style/XLStyle.cs
+++ b/ClosedXML/Excel/Style/XLStyle.cs
@@ -38,7 +38,7 @@
 
         private readonly IXLStylized _container;
 
-        public XLStyleValue Value { get; private set; }
+        internal XLStyleValue Value { get; private set; }
 
         internal XLStyleKey Key
         {
diff --git a/ClosedXML/Excel/Style/XLStyleKey.cs b/ClosedXML/Excel/Style/XLStyleKey.cs
index e68680d..46eea98 100644
--- a/ClosedXML/Excel/Style/XLStyleKey.cs
+++ b/ClosedXML/Excel/Style/XLStyleKey.cs
@@ -2,7 +2,7 @@
 
 namespace ClosedXML.Excel
 {
-    public struct XLStyleKey : IEquatable<XLStyleKey>
+    internal struct XLStyleKey : IEquatable<XLStyleKey>
     {
         public XLAlignmentKey Alignment { get; set; }
 
diff --git a/ClosedXML/Excel/Style/XLStyleValue.cs b/ClosedXML/Excel/Style/XLStyleValue.cs
index cec54b3..9135e5e 100644
--- a/ClosedXML/Excel/Style/XLStyleValue.cs
+++ b/ClosedXML/Excel/Style/XLStyleValue.cs
@@ -2,7 +2,7 @@
 
 namespace ClosedXML.Excel
 {
-    public class XLStyleValue
+    internal class XLStyleValue
     {
         private static readonly XLStyleRepository Repository = new XLStyleRepository(key => new XLStyleValue(key));
 
diff --git a/ClosedXML/Excel/Style/XLStylizedBase.cs b/ClosedXML/Excel/Style/XLStylizedBase.cs
index b4f43e1..307bcf7 100644
--- a/ClosedXML/Excel/Style/XLStylizedBase.cs
+++ b/ClosedXML/Excel/Style/XLStylizedBase.cs
@@ -8,14 +8,18 @@
     /// <summary>
     /// Base class for any workbook element that has or may have a style.
     /// </summary>
-    public abstract class XLStylizedBase : IXLStylized
+    internal abstract class XLStylizedBase : IXLStylized
     {
         #region Properties
 
         /// <summary>
         /// Read-only style property.
         /// </summary>
-        public XLStyleValue StyleValue { get; private set; }
+        internal XLStyleValue StyleValue { get; private set; }
+        XLStyleValue IXLStylized.StyleValue
+        {
+            get { return StyleValue; }
+        }
 
         /// <summary>
         /// Editable style of the workbook element. Modification of this property DOES affect styles of child objects as well - they will
@@ -78,7 +82,7 @@
 
         private static ReferenceEqualityComparer<XLStyleValue> _comparer = new ReferenceEqualityComparer<XLStyleValue>();
 
-        public void ModifyStyle(Func<XLStyleKey, XLStyleKey> modification)
+        void IXLStylized.ModifyStyle(Func<XLStyleKey, XLStyleKey> modification)
         {
             var children = GetChildrenRecursively(this)
                 .GroupBy(child => child.StyleValue, _comparer);
diff --git a/ClosedXML/Excel/Style/XLStylizedContainer.cs b/ClosedXML/Excel/Style/XLStylizedContainer.cs
index 7c8329e..04f94a7 100644
--- a/ClosedXML/Excel/Style/XLStylizedContainer.cs
+++ b/ClosedXML/Excel/Style/XLStylizedContainer.cs
@@ -6,7 +6,7 @@
     {
         protected readonly IXLStylized _container;
 
-        public XLStylizedContainer(IXLStyle style, IXLStylized container) : base(style.Value)
+        public XLStylizedContainer(IXLStyle style, IXLStylized container) : base((style as XLStyle).Value)
         {
             _container = container;
         }
diff --git a/ClosedXML/Excel/Style/XLStylizedEmpty.cs b/ClosedXML/Excel/Style/XLStylizedEmpty.cs
index dc7cdf3..931c4b4 100644
--- a/ClosedXML/Excel/Style/XLStylizedEmpty.cs
+++ b/ClosedXML/Excel/Style/XLStylizedEmpty.cs
@@ -4,7 +4,7 @@
 {
     internal class XLStylizedEmpty : XLStylizedBase, IXLStylized
     {
-        public XLStylizedEmpty(IXLStyle defaultStyle) : base(defaultStyle?.Value ?? XLStyle.Default.Value)
+        public XLStylizedEmpty(IXLStyle defaultStyle) : base((defaultStyle as XLStyle)?.Value ?? XLStyle.Default.Value)
         {
         }
 
diff --git a/ClosedXML/Excel/Tables/XLTableRows.cs b/ClosedXML/Excel/Tables/XLTableRows.cs
index bbc1479..f02dffa 100644
--- a/ClosedXML/Excel/Tables/XLTableRows.cs
+++ b/ClosedXML/Excel/Tables/XLTableRows.cs
@@ -9,8 +9,7 @@
     {
         private readonly List<XLTableRow> _ranges = new List<XLTableRow>();
   
-        public XLTableRows(IXLStyle defaultStyle) : base(defaultStyle.Value)
-
+        public XLTableRows(IXLStyle defaultStyle) : base((defaultStyle as XLStyle).Value)
         {
         }
 
diff --git a/ClosedXML/Excel/XLWorkbook.cs b/ClosedXML/Excel/XLWorkbook.cs
index f64c655..c9716be 100644
--- a/ClosedXML/Excel/XLWorkbook.cs
+++ b/ClosedXML/Excel/XLWorkbook.cs
@@ -52,6 +52,14 @@
             }
         }
 
+        internal static XLStyleValue DefaultStyleValue
+        {
+            get
+            {
+                return XLStyleValue.Default;
+            }
+        }
+
         public static Double DefaultRowHeight { get; private set; }
         public static Double DefaultColumnWidth { get; private set; }
 
diff --git a/ClosedXML/Excel/XLWorkbook_Load.cs b/ClosedXML/Excel/XLWorkbook_Load.cs
index 0d9de6c..85b6eec 100644
--- a/ClosedXML/Excel/XLWorkbook_Load.cs
+++ b/ClosedXML/Excel/XLWorkbook_Load.cs
@@ -2582,7 +2582,7 @@
                 {
                     LoadFill(fill, xlStylized.InnerStyle.Fill, differentialFillFormat: false);
                 }
-                xlStyle.Fill = xlStylized.InnerStyle.Value.Key.Fill;
+                xlStyle.Fill = (xlStylized.InnerStyle as XLStyle).Value.Key.Fill;
             }
 
             var alignment = cellFormat.Alignment;
diff --git a/ClosedXML/Excel/XLWorkbook_Save.cs b/ClosedXML/Excel/XLWorkbook_Save.cs
index 0b4dea1..59619b7 100644
--- a/ClosedXML/Excel/XLWorkbook_Save.cs
+++ b/ClosedXML/Excel/XLWorkbook_Save.cs
@@ -1883,12 +1883,12 @@
                 // https://github.com/ClosedXML/ClosedXML/issues/513
                 if (xlField.IsConsistentStyle())
                 {
-                    var style = xlField.Column.Cells()
+                    var style = (xlField.Column.Cells()
                         .Skip(xlTable.ShowHeaderRow ? 1 : 0)
                         .First()
-                        .Style.Value;
+                        .Style as XLStyle).Value;
 
-                    if (!DefaultStyle.Value.Equals(style) && context.DifferentialFormats.ContainsKey(style.Key))
+                    if (!DefaultStyleValue.Equals(style) && context.DifferentialFormats.ContainsKey(style.Key))
                         tableColumn.DataFormatId = UInt32Value.FromUInt32(Convert.ToUInt32(context.DifferentialFormats[style.Key]));
                 }
                 else
@@ -3211,7 +3211,7 @@
 
         private void GenerateWorkbookStylesPartContent(WorkbookStylesPart workbookStylesPart, SaveContext context)
         {
-            var defaultStyle = DefaultStyle.Value;
+            var defaultStyle = DefaultStyleValue;
 
             if (!context.SharedFonts.ContainsKey(defaultStyle.Font))
                 context.SharedFonts.Add(defaultStyle.Font, new FontInfo { FontId = 0, Font = defaultStyle.Font });
@@ -3406,7 +3406,8 @@
             {
                 foreach (var cf in ws.ConditionalFormats)
                 {
-                    if (!cf.Style.Value.Equals(DefaultStyle.Value) && !context.DifferentialFormats.ContainsKey(cf.Style.Value.Key))
+                    var styleValue = (cf.Style as XLStyle).Value;
+                    if (!styleValue.Equals(DefaultStyleValue) && !context.DifferentialFormats.ContainsKey(styleValue.Key))
                         AddConditionalDifferentialFormat(workbookStylesPart.Stylesheet.DifferentialFormats, cf, context);
                 }
 
@@ -3414,12 +3415,12 @@
                 {
                     if (tf.IsConsistentStyle())
                     {
-                        var style = tf.Column.Cells()
+                        var style = (tf.Column.Cells()
                             .Skip(tf.Table.ShowHeaderRow ? 1 : 0)
                             .First()
-                            .Style.Value;
+                            .Style as XLStyle).Value;
 
-                        if (!style.Equals(DefaultStyle.Value) && !context.DifferentialFormats.ContainsKey(style.Key))
+                        if (!style.Equals(DefaultStyleValue) && !context.DifferentialFormats.ContainsKey(style.Key))
                             AddStyleAsDifferentialFormat(workbookStylesPart.Stylesheet.DifferentialFormats, style, context);
                     }
                 }
@@ -3455,8 +3456,9 @@
             SaveContext context)
         {
             var differentialFormat = new DifferentialFormat();
+            var styleValue = (cf.Style as XLStyle).Value;
 
-            var diffFont = GetNewFont(new FontInfo { Font = cf.Style.Value.Font }, false);
+            var diffFont = GetNewFont(new FontInfo { Font = styleValue.Font }, false);
             if (diffFont?.HasChildren ?? false)
                 differentialFormat.Append(diffFont);
 
@@ -3470,17 +3472,17 @@
                 differentialFormat.Append(numberFormat);
             }
 
-            var diffFill = GetNewFill(new FillInfo { Fill = cf.Style.Value.Fill }, differentialFillFormat: true, ignoreMod: false);
+            var diffFill = GetNewFill(new FillInfo { Fill = styleValue.Fill }, differentialFillFormat: true, ignoreMod: false);
             if (diffFill?.HasChildren ?? false)
                 differentialFormat.Append(diffFill);
 
-            var diffBorder = GetNewBorder(new BorderInfo { Border = cf.Style.Value.Border }, false);
+            var diffBorder = GetNewBorder(new BorderInfo { Border = styleValue.Border }, false);
             if (diffBorder?.HasChildren ?? false)
                 differentialFormat.Append(diffBorder);
 
             differentialFormats.Append(differentialFormat);
 
-            context.DifferentialFormats.Add(cf.Style.Value.Key, differentialFormats.Count() - 1);
+            context.DifferentialFormats.Add(styleValue.Key, differentialFormats.Count() - 1);
         }
 
         private static void AddStyleAsDifferentialFormat(DifferentialFormats differentialFormats, XLStyleValue style,
@@ -4641,7 +4643,7 @@
                         maxInColumnsCollection = (Int32)col.Max.Value;
                 }
 
-                if (maxInColumnsCollection < XLHelper.MaxColumnNumber && !xlWorksheet.StyleValue.Equals(DefaultStyle.Value))
+                if (maxInColumnsCollection < XLHelper.MaxColumnNumber && !xlWorksheet.StyleValue.Equals(DefaultStyleValue))
                 {
                     var column = new Column
                     {
diff --git a/ClosedXML/Excel/XLWorksheet.cs b/ClosedXML/Excel/XLWorksheet.cs
index e9e1af5..b29631d 100644
--- a/ClosedXML/Excel/XLWorksheet.cs
+++ b/ClosedXML/Excel/XLWorksheet.cs
@@ -39,7 +39,7 @@
                 new XLRangeAddress(
                     new XLAddress(null, XLHelper.MinRowNumber, XLHelper.MinColumnNumber, false, false),
                     new XLAddress(null, XLHelper.MaxRowNumber, XLHelper.MaxColumnNumber, false, false)),
-                workbook.Style.Value)
+                (workbook.Style as XLStyle).Value)
         {
             EventTrackingEnabled = workbook.EventTracking == XLEventTracking.Enabled;