it says in the info good for -30f(
The rating is a military survival one and actually for only 4 hours sleep at -30F when used in conjunction with all the appropriate elements of the ECWS clothing as well all 3 parts of the sleep system. They are a good bag, and I was looking at them myself before I bought my own but they just were not big enough for me as I'm 6'5'' and could'nt find an extra long, but you need to read the whole blurb on the rating.