The ultimate sock for high altitude expedition use. Designed for hard shell mountaineering footwear and extended cold weather activities in extreme environments. Hand sewn and designed with specific left and right foot anatomical shapes for precise fit. This is the cutting edge of warmth technology. Based on feedback we received from professional mountaineers and cold-weather athletes we learned that most wool socks on the market were too constrictive and maintained moisture during their activities.This can be dangerous in parts of the world where a wet foot can lead to hypothermia or other serious conditions. Our design team wanted to solve this problem by creating a sock that would be incredible warm and dry. We searched the globe to find materials and a construction process that provide the perfect combination of elasticity, support, and warmth. We found that perfect combination in Polartec® Power Stretch and Primaloft Yarn.Two Layers of Polartec Power Stretch on the outer layer of the sock provide warmth without increasing weight. The smooth outer layer is wind- and abrasion-resistant; the soft inner layer pulls moisture away from your skin keeping you dry, warm and comfortable. The inner layer of Primaloft Yarn is made up of ultra-fine polyester fibers which are finer than cashmere, resulting in a luxuriously soft feel while providing unparalleled moisture wicking.When hiking, climbing or doing any aerobic activity, your body works up a sweat and emits heat and perspiration, but when you suddenly sit idle, you can easily start to freeze with an insulation that absorbs water. Primaloft fibers wick moisture away from the skin and trap body heat. Tested above 8,000 meters by athletes in real world conditions, you wont find anything else like these.