These bags worked great. I bought four of them for a recent camping trip that would be in the 30's. In 40 degree weather, we realized how warm they were and most of us unzipped the bags throughout the night. The next night, it got in the low 30's and the bag kept everyone toasty warm. I believe it would easily work into the 20's also - just wear a pair of long johns. Zipper works well and the bag is very comfortable yet light to carry. Fits well into the stuff sack. I've already recommended it to a friend. The bags also shipped quickly - I was surprised when they showed up in just a few days.