SealSkinz Mid Thermal Sock Using a high density loop pile padded layer of Merino wool as a lining, the Mid Thermal is the warmest SealSkinz sock available and is available in both black and olive green. Mid calf length. The Sock is Windproof, Waterproof, Breathable and can be used in MotorCycling, Fishing, Cycling, Outdoor, Equestrian, Military, Watersports.