The Men's Patagonia Nano Puff Vest is a sleeveless insulator for core warmth on the trails and around town. Pair with your preferred long sleeve, whether it's a base layer or flannel, and the 60g Thermogreen insulation will take care of adding the heat. Layer up in the cold, or stuff the lightweight vest into its own pocket and stash it away in your pack when the day heats up.