Don't go out on the mountain wearing cotton like you're going to the beach. Put on the Smartwool Merino 250 Baselayer Pattern 1/4 Zip Top instead, a baselayer made of warm, luxurious, and naturally odor-resistant merino wool. Clever seam construction keeps chafing to a minimum and adds a look of modern refinement to your mountain wardrobe. Smartwool's warmest baselayer is here to help you regulate temperature within cooler riding environments.