I haven't had a chance to test this bag down to the extreme rating of -10 degrees yet. I tried it at 3 degrees, without a tent or anything else, on a very cheap foam mat, wearing nothing but my boxers and socks and I was warm enough, so I'm very confident that with warm clothes and a good mat it will be warm enough at -10. (I also tried it at about 12 degrees and it is very breathable and I didn't get too hot. I am a 6 foot average sized male and thought that the width and length of the bag is perfect, it is very comfortable. A couple of very minor bad points: The drawstring for the shoulder and hood are on the same side, so it's a bit fiddly finding the one you want in the middle of the night, when your arms are in the bag. The mosquito net doesn't fold away very well and gets in your face a bit. Stitching on the stuff sack started to come undone on first use. Considering the price of the bag though these things are almost irrelevant. I would highly reccomend thi...