Build 4.0.0.5 of xlsgen improves how styles are managed internally, to avoid creating useless styles with operation such as Range.Apply() which is a mechanism used for copying or manipulating style and content in sheets. This is particularly useful if you are creating any substantial spreadsheet because of the limitation of Excel, which are 4000 for a XLS file and 50000 for a XLSX file. Note that when the limit is passed, Excel thinks the file is corrupt next time it opens it. Of course it isn't corrupt, it only has more styles that Excel decides it should have. With this build of xlsgen at least, we are doing our best avoiding the creation of temporary styles that end up being written in files.