Built for frigid late-season sits, the heavyweight Core Merino 330 Half-Zip features thewarmest-weight merino wool to keep you warm in the coldest conditions. Merino wool has an exceptional warmth-to-weight ratio to keep you warmer with less bulk and it regulates temperature through stop-and-go pursuits. Merino wool also resists odor to help minimize your scent, and theArmorSpun merino wool outlasts traditional merino wool. And to prevent sweat from leaving you wet and cold, Sitkaadded a synthetic interior that rapidly moves moisture away from your skin and through your system to keep you dry and warm.