ladridi

I am an ultralight backpacker, and the only bivy sack I have used so far is made by Adventure Medical Kits--it is called the Thermo-Lite Emergency Bivy, I think and weighs 7 ounces not including the stuff sack. It is water and wind-proof, but more importantly, costs around $20 US. It is not a space-blanket bivy, but does have similar thermal reflective properties in a stronger material. It also comes in a two person bivy and in a blanket. Check campmor.com for prices, etc.