Fourth Element Hotfoot ProFourth Element Hotfoot Pro With three layers of insulating fleece protecting the soles of your feet from the cold ground or boat deck, and a water resistant outer layer extending to mid calf, these are the warmest socks in our range. Featuring our unique thermocline fabric made using ECONYL recycled nylon, these socks are not only excllent thermal protection, but they are also part of our commitment to building a more sustainable product and company.