Stretch Fortius™ Air 20 fabric resists wind, and allows temperature-regulating air movement in the Arc'teryx Proton Men's Hoody, a “barely puffy” midlayer that uses CoreloftTM Compact 80 insulation to provide warmth. An insulation that resists packing out and allows warm air to pass thorough to maintain a consistent core temperature this is a lofty insulation with stretch. The front zipper is a No Slip Zip™ which you can lower to vent, and it will stay where you put it. As is fitting with a piece originally designed for climbers this has underarm gussets for improved range of motion and articulated elbows. An insulated hood with adjustment and binding to secure it around the face gives you added protection when you need it, and the chest pocket is sized to accommodate a radio. A trim fit for athletic performance this is designed to either be layered under a shell for cold or inclement weather insulation, or used as a stand-alone piece for extra warmth while you’re in motion in cold weather. A versatile piece designed to keep you comfortable when you’re out and moving in cold weather.