The Neutrino 400 offers low bulk and soft, lofty warmth with 400 grams of 800-fill down. It features Pertex Quantum fabric for lightweight durability, chevron and trapezoid box-wall baffles to eliminate cold spots, and an adjustable neck baffle for heat retention. The angled footbox provides a natural sleeping position. A zippered internal stash pocket secures essentials, and a waterproof roll-top sack protects the bag during transport.