diff --git a/src/Spout/Writer/Common/Helper/CellHelper.php b/src/Spout/Writer/Common/Helper/CellHelper.php
index 50ead93..9447252 100644
--- a/src/Spout/Writer/Common/Helper/CellHelper.php
+++ b/src/Spout/Writer/Common/Helper/CellHelper.php
@@ -61,7 +61,7 @@ class CellHelper
      */
     public static function isNonEmptyString($value)
     {
-        return (gettype($value) === 'string' && $value !== '');
+        return (gettype($value) === 'string' && $value !== '' && !$this->isNumeric($value));
     }
 
     /**
@@ -73,8 +73,7 @@ class CellHelper
      */
     public static function isNumeric($value)
     {
-        $valueType = gettype($value);
-        return ($valueType === 'integer' || $valueType === 'double');
+        return preg_match('#^-?\d+\.?\d*$#', $value) === 1;
     }
 
     /**
diff --git a/src/Spout/Writer/XLSX/Helper/StyleHelper.php b/src/Spout/Writer/XLSX/Helper/StyleHelper.php
index 4a13c95..04be6cb 100644
--- a/src/Spout/Writer/XLSX/Helper/StyleHelper.php
+++ b/src/Spout/Writer/XLSX/Helper/StyleHelper.php
@@ -151,6 +151,7 @@ class StyleHelper extends AbstractStyleHelper
 <styleSheet xmlns="http://schemas.openxmlformats.org/spreadsheetml/2006/main">
 EOD;
 
+        $content .= $this->getNumberFormatSectionContent();
         $content .= $this->getFontsSectionContent();
         $content .= $this->getFillsSectionContent();
         $content .= $this->getBordersSectionContent();
@@ -165,6 +166,21 @@ EOD;
         return $content;
     }
 
+    /**
+     * Return the content of the "<numFmt>" section
+     *
+     * @return string
+     */
+    protected function getNumberFormatSectionContent()
+    {
+        $content = <<<EOL
+<numFmts count="1">
+    <numFmt formatCode="$#,##0.00" numFmtId="164"/>
+</numFmts>
+EOL;
+        return $content;
+    }
+
     /**
      * Returns the content of the "<fonts>" section.
      *
@@ -298,8 +314,9 @@ EOD;
     protected function getCellXfsSectionContent()
     {
         $registeredStyles = $this->getRegisteredStyles();
+        $countStyles = count($registeredStyles) + 1;
 
-        $content = '<cellXfs count="' . count($registeredStyles) . '">';
+        $content = '<cellXfs count="' . $countStyles . '">';
 
         foreach ($registeredStyles as $style) {
             $styleId = $style->getId();
@@ -323,6 +340,9 @@ EOD;
             }
         }
 
+         // Add default style for numberFormat
+        $content .= '<xf numFmtId="164" borderId="0" fillId="0" fontId="0" applyFont="1" xfId="0" applyNumberFormat="1"/>';
+
         $content .= '</cellXfs>';
 
         return $content;
diff --git a/src/Spout/Writer/XLSX/Internal/Worksheet.php b/src/Spout/Writer/XLSX/Internal/Worksheet.php
index 029c115..e54119a 100644
--- a/src/Spout/Writer/XLSX/Internal/Worksheet.php
+++ b/src/Spout/Writer/XLSX/Internal/Worksheet.php
@@ -238,6 +238,8 @@ EOD;
      */
     protected function getCellXML($rowIndex, $cellNumber, $cellValue, $styleId)
     {
+        // If $cellValue has double format then assign style from numFmt section (2) else default (1)
+        $styleId = preg_match('#^\d+\.\d+$#', $cellValue) === 1 ? 2 : $styleId;
         $columnIndex = CellHelper::getCellIndexFromColumnIndex($cellNumber);
         $cellXML = '<c r="'.$columnIndex.$rowIndex.'"';
         $cellXML .= ' s="'.$styleId.'"';