Introducing the Lenz Heat Sock 5.1 Toe Cap, the newest and most innovative way to keep your feet warm this winter. These socks are slim fit, catering to smaller calves and allowing for easier entry and exit from ski boots or hiking boots. Offering a seamless fit for long lasting wear, they are made with a high-quality blend of some of the finest materials, including merino wool, polyester and a touch of silk. For reliable warmth, whether you’re riding the chairlift or hiking through the snow, they come with a Lithium Pack rcB 1200 Battery, meaning they are compatible with the Bluetooth smart-phone accessible lithium pack rcB 1200 battery pack with 14 hours of heat generation. If you run extra cold and prefer additional hours of operation, the lithium pack rcB 1800 provides up to 20 hours of heat. Each with three different settings, you can adjust to your personal preference. With the Lenz Heat Sock 5.1 Toe Cap, you'll enjoy all-round heat from the top and bottom, thanks to the special Toe Cap that heats from both sides. The lithium pack battery sits beneath the special comfortable leg band such that you hardly notice it, making it perfect for those long days on the slopes or just out and about in cold weather.