The Marmot Lassen Polartec Beanie regulates our body temperature during high-output activities in cold weather. Perfect for winter hikes and trail runs, the lightweight fleece keeps our domes warm while wicking sweat, so we don't get too cold or too hot and sweaty. The low-profile design is also made to fit under a helmet in case we need a little more insulation when we're skiing or fat-tire biking.