Whether we're sneaking in a few last hikes in the late fall before snow starts falling or riding over open groomers on frigid winter days, the Smartwool Classic Thermal Merino Base Layer 1/4-Zip Top offers next-to-skin comfort and plenty of warmth so we can continue getting outside as temperatures drop. The Merino wool construction is warm and breathable, perfect for high-intensity activities in cool weather, and it's naturally odor-resistant for a fresh feeling that lasts all day.