The warmest socks in this Fourth Element range and arguably the warmest on the market, the Hotfoot Pro Socks have three layers of insulating fleece protecting the soles of your feet from cold surfaces along with a water resistant outer layer which extends to mid calf. These socks are not only excellent thermal protection, but they are also part of our commitment to building a more sustainable product and company, as they feature Fourth Element's unique thermocline fabric made using ECONYL® recycled nylon.