A great choice for backcountry pursuits, the Arc'teryx Boys's Delta AR Zip pullover offers a superb warmth-to-weight ratio. This is due to the fabric choice for this garment, the Polartec Thermal Pro high loft grid that traps plenty of heat without the bulk. Also, it has a trim fit so it layers well and thus there's not a bunch of Additional fabric to haul around when not in use.