The 1000 Mile Ultimate Heavyweight Walking Sock uses the 1000 Mile double layer system to help reduce friction on the skin The 100 Tactel reg inner stays with the foot wicking away moisture whilst the soft wool-mix outer layer moves with the shoe The lack of friction between the layers helps to prevent blisters and reduces wear This sock is designed to be thicker than the 1000 Mile Lightweight Walking Sock to provide added volume insulation and warmth Ideal for 3 and 4 season walking in all boots