Arc'teryx Atom SV Hoody Size LAtom SV Jacket: Our warmest Atom jacket for cold weather hiking Atom: Versatile synthetic insulated mid layers with a high degree of weather resistance. Severe Weather: Most durable materials and weather protection, for prolonged exposure to severe conditions. Synthetic Insulation: Man made insulation with quick dry times, durability and retains warmth when damp. Multi Use: Versatile high performance designs for diverse activities and conditions.