I have one of the older, rectangular models. I was planning on using it as a ground sheet under a new tarp, 15 years ago. The first night out, it was unexpectedly rainy and cold, so I put my pad whole sleep system inside the bivy and slept warm and dry. Since it was just an overnighter, my biggest concern was that I looked like a Chipotle burrito for the cats in the area. If it were a longer trip, I'd have been more worried about condensation.