The Midweight Crew is made from SmartWool's heaviest NTS fabric. Warm, yet still breathable for stop and go activities, it's ideal for cold weather. Next to Skin NTS midweight 250 base layer works alone or as a cold weather base layer. Made from pure merino wool for softness and warmth. SmartWool breathes, manages moisture vapor, and regulates temperature to keep you dry, comfortable, and warm. Naturally resists odor. Fine merino wool fibers do not itch. Interlock knit 50 UPF for sun protection. Back body seam wraps to front for body enhancing fit. Shoulder panels eliminate top shoulder seams for nonchafing comfort when wearing a pack. Flatlock seam construction eliminates chafing. Heat transfer logo at left sleeve cuff. Form fit: follows the contours of the body.