I am generating an excel file on demand, then zip that with other files and then write that in the response stream so the user is prompted with the download dialog. The problem is that the response stream is opened right at the beginning but nothing is written until the files are completed so if that takes a long time, there is a timeout and the downloaded zip has 0 kb. A workaround was to make a readme file and write that in the stream right away so the download begins and and something is actually is written in the response to prevent the said timeout. This works on Firefox but in IE, if the readme is too small, the download doesn't start. Is there a browser internal buffer that causes that ? Can I set something in the header of the response to prevent that ? Thank you.