"I rarely took this jacket off," raves a tester who wore the Atom as an outer shell and as insulation. He credits the strong breathability and easy layering, both the result of a hybrid design that combines compressible Coreloft insulation in the torso, arms, and hood with side panels of Polartec Power Stretch. You get warmth without bulk (it slides easily under a shell) and venting superior to any other puffy jacket.
"I didn't get hot when snowshoeing up the steeps because the fleece sides were so breathable," says a tester. As an outer layer, the water-resistant nylon shell shed snow and dried quickly when damp. A sculpted "scuba" hood boosts warmth by wrapping far forward around the face. The hood is designed to be worn under a helmet, so it has no drawstring; as a result, it flopped a bit in the wind when worn alone. Fit is trim. $199; 12 oz.; men's S-XXL, women's XS-XL; arcteryx.com