Stay cozy and at ease. The patented Toe Cap heating element ensures all-around warmth, heating toes from both above and below. The heat sock 5.1 toe cap slim fit knee socks are perfect for those with narrow feet and legs. They're ergonomically knitted for a perfect fit, with a ring bandage for a comfortable foot hold. Shin protectors and reinforcements on toes and heels prevent pressure points. The skin-friendly blend of merino wool and silk is breathable, quick-drying, and comfortable. A light, rechargeable lithium pack battery can be optionally purchased and is barely noticeable under the special comfort cuff. Heat can be controlled directly on the lithium pack or via the free Lenz heat app on your smartphone.