The human body uses energy to keep warm. PrimaLoft uses a patented microfiber structure to help the body retain warmth and conserve energy. PrimaLoft is as warm as down, compressible, breathable and offers superior water repellency so you remain dry, warm and comfortable even under the most extreme conditions. These performance qualities and technical benefits make PrimaLoft the thermal insulation of choice for outerwear, gloves, footwear, and sleeping bags.