As I needed to export some data to an xlsx (Excel 2007+) file.
I first used the Microsoft OpenXML library called DocumentFormat.OpenXML.

At first it looked good but it had some major performance issued while using the object oriented style. I switched over to the OpenXMLWriter (SAX) but this introduced another class of problems like corrupted files. The Documentation is a pile of shit and a while I gave up and reimplemented my export with NPOI.

To have it a little simpler i wrote some helper functions to do the cell and row injection. The result is as follows.