The Smartwool Classic Thermal Merino Base Layer Crew - Women's is a Merino wool base layer for staying warm when exploring the cold. Ski days, hiking weekends, cold weather camping and so much more. This first layer keeps the heat in and comfort levels high. The slim fit allows for the easy addition of layers over top, while flatlock seam construction prevents chafing. The 100% Merino wool fabric breathes to prevent overheating, provides thermoregulation, and resists odors for a super comfy time outdoors.