Dang, you read my mind. Actually I was going to replace my tyvek floor on my tarp with polycro to save a few ounces but then I thought I might be able to make my own tarp thats 8oz. Ditch my sleeping pad for reflectix. Get a Zpack arc blast. Bamm!! Then my base weight would be around 4lbs. Ok, back to reality, not buying a Zpacks arc blast. Just bought a Osprey exo 38. Happy with a 6 pound base but I am really thinking about making my own tarp out of polycro