Midlayer or standalone, the Atom Vest is a proven performer across a range of seasons, landscapes and activities. With its most advanced insulation, fabrics, and design ever, this evolution builds on its legendary performance. Coreloft™ Compact insulation retains warmth if wet and withstands years of packing and unpacking, and the breathable, durable Tyono™ 20 shell resists wind and light weather. Stretch fleece side panels aid ventilation and freedom, and the entire vest packs into its own pocket.