I'm trying to look into TYVEK right now. It's the white plastic looking stuff you see wrapped around new houses before the siding goes up. I've read some really good reviews on the backpacker mag website about this stuff. Very light, very strong, looks like plastic but is more akin to gortex (waterproof but breathable). It comes in 9 foot wide rolls. Best price I have found so far is $115. for 195 feet (of course, you could pay that much for a good quality tarp). I'm having trouble finding a source for anything less than a full roll so that I can try it as a tarp and then see if I can make a tent out of it. The one major down side that I have heard is that it is white with "3M" or "housewrap" written on it and you can't change it's appearance.