We use these for skiing and they are great! Just make sure to put the shiny side down. Also as you are putting them in your boots - don't wait too long between opening the package and putting them in because they can poof up (but that goes away after you put your foot on them and put weight on them). The M/L fits my shoes (women 9) and my husbands (men 9) great.
The first time I used the warmers, my feet became Happy Feet! Have not tried them for very cold climate yet...32 degree night only thus far. Will update review after weekend in January in NYC.
I purchased these for my husband to replace some worn out boots. He wears them on a motorcycle and says the soles are very grippy and comfortable to ride in. He's worn them riding in the cold down to the 30s and has said his feet were warm the whole time. I bought them because they are waterproof and they come in wide sizes. So far they hold up great in harsh weather. and I hear nothing but raves. I'd definitely recommend them.
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