You won't believe how much warmth and comfort you get from such a small package - the Nitro packs into a tiny sack (included), but stays toasty to 15 degrees. We build in Flex™ between the shoulders and knees, so you get the comfort and thermal benefits, while saving precious ounces. Continuous baffling and a draft tube contain 800-fill goose down, the warmest, lightest insulation available.