Arc'teryx Atom LT Vest - Women's This sleeveless core-heater hugs the body with efficient Coreloft(TM) insulation to preserve warmth while smooth faced, air permeable, fleece stretch side panels increase ventilation. A wind and moisture resistant outer shell extends stand-alone usability. Features: ATOM - Versatile synthetic insulated mid layers with a high degree of weather resistance. LIGHTWEIGHT - High performance, minimalist design that is durable for its weight. ARC'TERYX ESSENTIALS - Versatile high performance designs for diverse activities and conditions. SYNTHETIC INSULATION - Man-made insulation with quick dry times, durability and retains warmth when damp.