Just to add, I have a WM bag that weighs one pound and is rated, I believe, at 40F (maybe 35). One day in Maine I forgot to bring in my water bottle. I was wearing everything in my pack, but I was toasty warm when I woke up and found there was ice in my water bottle. Didn't have the thermometer that day, but it takes more than just 32F to freeze a water bottle, so I'd say it had to be at least 30F. best, jcp,