Midlayer Or Standalone, The Atom Lt 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.