Anyone working in cold country knows just how miserable life can be when your feet feel like blocks of ice. These ThermaCELL heated insoles, which replace the insoles that came with your boots, rely on built-in lithium-ion batteries that eliminate the need for a separate battery pack and old-school wiring. Batteries are controlled with a remote you can slip in your pocket to provide no heat, low heat (100 degrees F) and high (110 degrees F)—just warm enough to keep your feet comfortable without making them sweat. Batteries provide 5 hours of warmth, and take four hours to recharge (batteries can be removed from the insoles for recharging without taking the insoles out of the boots). ThermaCELL offers two versions: the original and ProFlex models.