Designed as an active-use insulation layer, the lightweight and compressible Atom LT Jacket from ARCTERYX offers maximum warmth with minimal weight and can be worn as a stand alone or for layering under a hard shell. Made to provide core warmth and mobility with thermally efficient Coreloft insulation in the torso and arms and moisture-wicking, breathable, stretchy Polartec PowerStretch at the sides and underarms.