Hotronic’s heated insoles are some of the best on the market. The S3 Custom product is more affordable compared to Hotronic’s S4 Universal. Batteries last significantly longer as well, with up to 17 hours of continuous heating.
Hotronic S3 Power Plus Boot Heaters provide on-demand warming to your feet and toes. Battery pack secures to the back of your boots and slides under the cuff of your pants. These heated insoles are easy to install and use.
Four temperature settings are available with these electric insoles. Low setting heats to an average of 84-95°F and lasts 14-17 hours. Second setting heats to 107-118°F and lasts 5 to 7 hours. Third temperature level heats at 122-132°F lasting for 3-5 hours. And highest heat level warms to 156-168°F lasting for 2-3 hours. Heating element is near the ball of the foot.
Main difference between S4 and S3 electric heated insoles is the battery life. Besides that the products function the same.
Hotronic “Universal” models come with a trimmable insole. You trace your existing insole over the Hotronic one and trim it to the correct size. “Custom” models don’t come with a trimmable insole. Instead you only get the heated pads and adhesive strips. The benefit to Custom models is the fact you can use it with custom orthotics insole.