I have always struggled to keep my feet warm during hunting. I have several pairs of Kenetrek boots, uninsulated, as well as 400 grams of insulation and 1000 grams. Even with the 1000 gram pair, my feet have not stayed warm. I have tried these and they seem to definitely help. Have not had them out as many days as I would like for a detailed evaluation, but they appear to make a big improvement.