Sock for the extreme cold with an anatomical design (left/right foot) and three layers of fabric in the foot made up of two layers of Polartec Power Stretch® multi-elastic fabric with a Primaloft® insulation layer in the middle. 78% Polartec Power Stretch®,11% Primaloft®, 8% Nylon, 2% Thermolite®, 1% Stretch Nylon with Lycra®