I have a bivvy with a "water resistant" top and coated bottom from OR that perhaps unfortunately, is discontinued. Condensation has never been a problem, and I've used it on some warm nights, cold nights, etc.

I hear that waterproof-breathable fabrics do vary significantly in breathability. I have an early Goretex knock-off tent that I don't think breaths well and sometimes has caused a slight problem (because tent is very very small).


For me, this factor is less significant in rainwear, but I'd want as much breathability as possible in a bivvy sack.

Unfortunately I can't remember the one everyone seems to prefer. Nextec? Epic? I don't remember......It's expensive whatever it is....The army tested various fabrics in their lab in Natick, Mass., and one came out on top.