Originally designed, tested and adapted by the U.S. Military for use in all-weather conditions and our 2 sock system allows you to use the same sock for any environment, from a mountainside with sub-zero temperatures to a desert plain with temperatures of +120 Fahrenheit. Our 2-part system is designed to prevent friction, provide insulation and reduce moisture build-up. The high density nap construction of the boot sock provides maximum comfort on all types of terrain and in all weather conditions. Choose from our Techspun Extreme Weather (EW) or All Weather (AW) options. Both are ideal for all weather conditions and provide ultimate protection for your feet.