These things work as expected. The intent is to keep your feet at body temperature. I just used these over the weekend on days where the temperature was ZERO... they worked. I like the fact there are no wires (I have ski boot heaters with wires and BIG batteries). The smartest way to use these insoles is to put them on medium to get the maximum time.
My husband is a hunter and when you hunt in ND at this time of the year, your feet get cold when you are out for extended periods of time. He has enjoyed the warmth of these inserts and will be happy to have them when he is our snow-blowing too!
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