I have the same Bivy. The adventure medical SOL heat sheets bivy. I used it use while camping in the Rockies during fall. I figured it was September and couldn't get too cold, so I packed a small summer sleeping bag. Wasn't nearly enough, it dropped down to freezing at 9,000+ feet. I didn't think about the altitude or the latitude. The bivy made sleeping much easier. The sleeping bag was only rated to 32F. And we all know the ratings are lies.