This light weight sock is made from the high performance yarn PrimaLoft Spin. Constructed with a special front vamp to eliminate bunching at the ankle and a cushioned sole for shock absorption and insulation. Designed with super stretch ribbed leg and welt to prevent muscle fatigue and pinching. The Sierra is super soft, a moisture mover and thermal insulator - an absolute in performance and comfort. 38% nylon, 30% PrimaLoft polyester, 30% merino wool, and 2% spandex.