[FOSDEM] Paper in floor

Hello! @FOSDEM in the floor you can find grey paper where everybody can draw. I found this Photo: http://www.vuntz.net/photoblog/20070228_FOSDEM-notes-bad.jpg there you can see this grey paper. Can somebody tell what is the name of this paper? I would like to buy, but can't find it... thx Walery ;o)