If you will take the trouble to buy two of the "heavy duty" types, with the gunny sack material glued on the back of the mylar, lay down on them and cut out a 'mummy" configuration, glue and sew 3/4" wide velcro all the way around, use a silk bag liner, wear Goretex cammies (or wool OD greens) and Thermax Expedition wt long johns, you can sleep in this bag just fine, at 20+ degrees F, inside of a 2 poncho "tent", suspended between 2 trees, in a hammock that is similarly suspended. The Mylar tears are easily taped, and it doesnt get soaked, or lose its stuffing, and there's no zippers to get jammed or break.