This T3 Midweight Hiking Sock features 3 separate layers of fibers that work together for comfort, warmth, and moisture management. The layer of PrimaLoft Eco® is made up of fine fibers that form tiny air pockets to trap body heat and keep the cold out. The result is immediate warmth without the bulk. These fine fibers are engineered for permanent water resistance and create tight surface tension that resists moisture penetration. A layer of Merino Wool provides added warmth and softness agains"t the skin. Lastly, a layer of Nylon and Ea. LYCRA® adds durability and ensure these socks stay up in your hiking boots without slipping down to your toes. The Mid Weight Hiker has medium cushioning all around the sock so that they fit snuggly in hiking boots and protect the foot from irritation.