Performing as midlayer and standalone across a broad range of activities and output levels, the iconic Atom is an Arc‘teryx mainstay. Its Coreloft Compact insulation retains heat when wet and withstands repeated packing and unpacking. Light, soft and durable, the Tyono 20 face fabric resists wind and weather, and stretch fleece side panels improve ventilation and freedom of movement. Size and Fit Tips: The Atoms offer more room in the body than their predecessors, the Atom LTs, for improved comfort, versatility, and freedom of movement. Fitted Fit - This trimmer fit is patterned to stay close to the body through the chest, waist, hip, and thigh. Its low profile eliminates bulk, moves with the body, and fits comfortably over our first layers. This model's fit has evolved.