Marmot Helium Sleeping Bag Light Enough to Forget, Warm Enough to Count On When the temperature drops well below freezing and every ounce in your pack matters, the Helium earns its place. It's a genuine three-season mummy bag rated to 15degF, built around high-fill-power goose down treated with Expe DRY water-repellent finish so it keeps lofting even when conditions get damp. The Pertex(R) Quantum outer fabric traps still air and sheds light moisture without adding bulk. An anatomically designed wrap-around footbox and smooth curved baffles keep the down where it belongs through the night. Features850-fill-power RDS-certified goose down high warmth-to-weight ratio in a compact, packable mummy Expe DRY water-repellent down treatment resists moisture, maintains loft, and reduces dry time versus untreated down Pertex(R) Quantum outer fabric traps still air for insulation efficiency while keeping weight low Anatomically designed wrap-around footbox with smooth curved baffles seals warmth at the foot end and prevents down from shifting | Marmot | Helium Sleeping Bag