Breathable socks with a tight fit; Quick and easy attachment of batteries with snaps; Heel and toe reinforcements; Heat Fusion technology for diffusion and heating all around the toes; Composition: 49% Acrylic, 27% Polyamide, 10% Merino Wool, 12% Polypropylene, 2% Elastane; S-Pack battery keeps your feet warm for up to 8/14 hours; Pack includes two rechargeable batteries; USB charger included; Wall charger NOT supplied