Used this bag for the first time last weekend. It was 15 degrees on Friday night and 25 degrees Saturday night. I slept on a 1.5" air mattress with the reflective side up of a survival blanket under the mattress. I was so warm that I took off my long underwear and slept nude. I wore a polarfleece tobogan on my head. I never got cold all night at these temperatures. If it went to zero outside, I may need the long johns. One downfall is the pack size. It is a little large for backpacking but not out of the question. I would pack it for the warmth. Very nice bag for the money. Well constructed