i perspire relatively lightly. after a night of light snow, and the storm flap only covering my head (not zipped), i had very little condensation inside the sac come morning. my buddy sleeping in an older sac and of less quality, arose with significant moisture on his sleeping bag, (he sweats a lot) it has easy access and zips well. i appreciate the no see-um bug mesh. it would be nice to have a window in the storm flap to see the stars, snow or whatever. overall, i'm quite pleased with this product, enough that the use of my tent is now limited

If your venturing into bivy terrain don't leave home without this. I've used mine a lot and have had great luck. It is a little heavier than some of the ultra lights on the market, but worth the extra weight. I've used some lighter ones and they can be one use wonders - light, but not at all duragble and they don't breath. This bivy sac breathes really well and will stand up to multiple season of use. Well worth the extra cost. Overall a great product.

I am wildland firefighter and spend MANY nights sleeping on the ground(pretty much all summer). The first time I used this was on a fire in Santa Cruz, cold night and woke up soaked! I thought I just had too many layers. Next night slept with nothing on and still woke up soaked! Such a bumber to pack a wet sleeping bag into a stuff sack for the day. Im sorry to be a downer, but I DO NOT recommend this bivy!