I have two, one's a surplus military mummy bag, which is fine down to about zero, and an Alaskan Sleeping Bag, bag, good to -40 or something. It has goose down in it, I've slept out on the snow in it. the mummy bag is down and feathers, and works well. I once slept under a picnic table in Yellowstone park, in it, and it snowed that night, and was totally comfortable.
