Move over down and polyfil, and make room for the new kid in town. The SmartWool Men's PhD SmartLoft Divide Full-Zip Top maximizes the versatility of merino wool to keep you warm from your first fall hike through your last spring ski trip. Wear this zip-up as a super-heavyweight baselayer when you're climbing in extreme conditions or wear it by itself at the tail of April showers, and let the DWR-treated front panel shield you from wind and light drizzle. Behind that nylon, SmartLoft insulation keeps your core warm with its proprietary combination of wool and polyester that regulates your temperatures better than all-synthetic insulation and, unlike wool, keeps warming when it's wet. On the arms, sides, and back, a double layer of merino wool jersey offers intelligent protectino from the elements when you're working hard. Lined entirely with soft merino wool, this jacket won't leave you an itchy wreck if you're only wearing a tank top underneath.