Heat Jammer Brushed Thermal Thick Warm Hiking Cushion Socks Pack of 6 2% polyester Imported ******1.26 CLO Rating****** CLO is the unit used to measure the ability of a garment to retain heat according to Nord American standards ASTM1291. The higher the CLO rating, the better a garment is at retaining heat. Non binding top provide relief for cold feet caused by circulation problems, Thick cushioning with intensive brushing technique provide maximum heat retention and comfort, Reinforced heel for better fit, Super softness shape retention for long wearing, High bulk yarn construction for maximum heat retention,