A great insulated top that can be used as outerwear or as a mid-layer, the Men's Nano Puff Pullover from Patagonia is a warm, lightweight, compressible shirt that is insulated with PrimaLoft synthetic insulation. The Deep center front zipper makes layering easy and allows you to vent quickly when working up a sweat. Patagonia has also given the Nano Puff Pullover a zip chest pocket and at only 10 ounces they have kept it as light as possible. PrimaLoft insulation will provide great insulation and continues to provide warmth even when wet.