Every foot shape is different, and sometimes you'll need a little extra help making your boots as comfy as possible. Insoles prevent your foot from slipping around in any extra space there might be inside the boot, therefore stopping rubbing and blisters.
If you've bad circulation or a heightened sensitivity to the cold, heated insoles could be the answer to an uncomfortable and possibly debilitating condition. Just pop them into the bottom of your ski boots and you'll have toasty feet for hours!