For the sock wearers who want a blend of quality materials and innovative technology, the Lenz Heat Sock 4.1 with Lithium Pack rcB 1200 battering combines comfort and warmth with performance. Athletes who spend long hours outside braving the winter elements will love the Polyester/Polyamid material with a touch of wool, eliminating moisture and keeping feet dry and temperature regulated. For maximum warmth, these socks pair with either the Bluetooth smart-phone accessible lithium pack rcB 1200 battery pack providing 14 hours of heat or the lithium pack rcB 1800 with 3 settings for up to 20 hours of heat. Depending on your preference and level of activity, you have the option of choosing, and how cool is that? Heated socks are the next best thing in the world of winter sports, and these socks do an excellent job proving that. Want to heat your left foot more than your right? Not a problem. Worried about a bulky battery pack getting in the way? Not with these. Sitting seamlessly beneath the special comfortable leg band so you can get in and out of your ski or hiking boots with ease. The latest in heating products, the Lenz Heat sock 4.1 will keep you active all winter long.