Only Worn Once. Perfect condition. Built for frigid late-season sits, the heavyweight Core Merino 330 Half-Zip features our warmest-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 our ArmorSpun merino wool outlasts traditional merino wool. And to prevent sweat from leaving you wet and cold, we added a synthetic interior that rapidly moves moisture away from your skin and through your system to keep you dry and warm.