This Mid-calf-high waterproof sock is insulated with a liner made of expedition-weight double velour Polartec® Power Stretch™ fleece (7.3 oz. Per square yard). The outside layer is knit of nylon/lycra® spandex offering a durable, flexible, stretch covering. In between the two fabric layers is a waterproof MVT membrane. These three layers are securely bonded together throughout. This combination of materials provides a very soft, comfy, warm, stretch-to-fit sock suitable for a whole host of cold, wet, nasty outdoor conditions. If you are outside in cold weather doing such activities as hunting, ice fishing, skiing, boating, and military service – you will be pleased with these socks.