If you need a reliable base layer for cold weather running, skiing and all of your other winter adventures, you can’t go wrong with the Smartwool Classic Thermal Merino Base Layer Crew. This might be the perfect base layer for running during the winter. It’s made with 100% Merino wool that’s naturally moisture-wicking, odor-resistant and temperature-regulating, so it’s great to wear next to your skin under other layers. Details: 100% Merino wool fabric made with an interlock knit for enhanced comfort, breathability, thermoregulation and odor resistance Fit updated to improve functionality while enhancing aesthetics Shoulder panels eliminate top shoulder seamsFlatlock seam construction designed to minimize chafing