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