The Nano-Air Light Vest was made to be worn for the entirety of your aerobic, start-stop mountain activities, so you're never slowed down by having to change layers. Stretchy and breathable FullRange insulation dumps excess heat when you're working hard and keeps you warm when you're not. | Patagonia Men's Nano-Air Insulated Light Vest in Glacial Blue, Large - Recycled Polyester