I bought these as a stocking filler for my husband as he was always complaining of cold feet whilst out on his bike. He was so impressed with them that, when he ran out, he bought some for himself of a different make because he couldn't find these. He discovered that it was best to leave them out of the packet for a up to a minute, before putting them on his socks, to allow them time to heat up. They do work, if put on straight from the packet but don't become as warm. He loves them and now never complains of cold feet. He's going back to Toastie Toes though because the others didn't become as warm nor did they last as long. I guess it all depends on how air tight the shoes are.