I bought a pair of these this year, and am still up in the air on them, I have wore them 3 sits
-first sit my boots were wet and cold when I put them on and they didn't help at all
-second sit, i put them on before my feet got cold and they seemed to help some
-third sit put them on over wet cold boots and threw a handwarmer in the toes, and they worked wonders
the second time I used them, the zipper broke on the back of one of the boots