Hotronics One-Size-Fits-All insoles are
flat insoles which you install the Hotronic heating elements neatly into the toe area. All you do is trim the insoles to the size you require. You'll receive 2 insoles that are about 1/8 inch thick.
This is a great way to add heat to a second pair of boots or shoes and share the same batteries. All you need to order are the heating elements.