StringBuilder can not export to anything, it is for string building. That's all.
AppendFormat[
^] is not for cell styling or anything that like.
- If you build a CSV file for example, than you can not add any styling.
- You can use OpenXML format if you have Excel 2007 and above or FileFormatConverters on Excel 2003:
http://closedxml.codeplex.com/[
^]
- A simple trick is to make a html with a styled table in it and name it xls. Excel will open seamlessly. (You might get a warning, but that's all)
- You can use Excel-XML format also:
http://www.openscope.net/2010/02/09/transforming-xml-into-ms-excel-xml/[
^]