Everybody knows that xenon gas is being used as the propellant for ion thrusters in spaceships, but few people are aware that it's also used as the insulator in Marmot's 15 Degree Down Women's Xenon Sleeping Bag. What's that, science master' Fine, it isn't actually, but the 850 fill goose down that Marmot chose is a way better insulator anyway. Plus, when you combine with a DWR coated Pertex Microlight shell, the whole bag weighs a lightweight 2lbs 9oz, so it won't sit like a boulder in your backpackmaking it perfect for all spring, fall, and moderate winter trips. The insulation itself is treated with Down Defender, a water repellent coating that helps it maintain its loft and warmth, even if it does get a little bit wet there's actually extra down packed into key areas, making sure you don't have to deal with cold spots. There are strategically placed stretchy baffles as well, which move with you to keep you comfortable while you're dreaming and, since drafts have ruined many an otherwise cozy night, the Xenon has an insulated draft tube, collar, and face muff to keep all the cold air out and the warm air in.