Smartwool long sleeve base layer in sunset coral palm Smartwool says: Meet the Women's Classic Thermal Merino Base Layer Crew. This top is 100% Merino wool fan favorite and features an enhanced fit to improve functionality while elevating aesthetics. The addition of shoulder panels and its flatlock seam construction help prevent chafing and increase your comfort level. Add one of our best base layers for cold weather to your winter wardrobe and experience the difference the next time you go skiing, hiking, climbing, or biking.