It’s easy to make a warm jacket for biting cold or an airy one for mild temps. It’s the conditions in between that are a challenge. The Nano-Air Light handles both sides of the coin—like climbing hard in a predawn chill—with an insulated front and breathable back. Its hybrid construction packs 40 grams of synthetic insulation that stretches as you move on the torso, while waffle-knit fabric on the back and under the arms sheds heat. A DWR-coated ripstop nylon shell with four-way stretch shakes off light moisture with ease and provides supreme mobility.