I purchased these to replace the ridiculously uncomfortable liners in my military issued extreme cold/wet weather boots.  I have not been disappointed!  There is occasional slipping so that I can feel the seam, but this can be prevented by pulling the warmers tight before putting my feet into my boots.  Since they are micro fleece, they don't retain very much moisture/sweat, and when combined with a moisture-wicking synthetic sock, my feet remain fairly dry and warm even after spending most of the day inside a heated building.  Once a week I throw these into the wash so that they don't stink.  Great product.  I will buy these again when the first pair wears out.