Trust me on this one, haul out your yellow pages, look up sound, sound systems, sound pros, etc. Give anyone of them a call and ask if they have sonex or some other high quality acoustic foam, they should have anything from 4'x4'x4" to 2'x2'x1" panels. The thicker the foam, the better it does at reducing lower frequcnies, for case fans, 1" or 2" is plenty good. With sonex you do get quality stuff but its pricey, so if they have something that performs just about as good and is 50% less, get the cheaper stuff.