Cotton Imported WARMEST THERMAL SOCK: Heat Holders are the warmest thermal socks Heat Holders offer and are 7X warmer than a basic cotton sock SUPER SOFT: Our thick winter socks keep you warm and comfortable DIABETIC FRIENDLY: Heat Holders are made with a patented loop technology that allows for enhanced warmth and are made with a non-binding top for a comfortable fit VERSATILE COLD GEAR: Our crew thermal socks are made of 91% acrylic, 5% nylon, 3% polyester, 1% elastane for the ultimate combination of warmth, softness, and comfort HEAT HOLDERS: Heat Holders make socks in three different levels of warmth to fit whatever your day may bring