The boots are OK in regards to keeping your feet warm. I've worn better and worse. Fortunately my feet don't get cold easily, so I don't have a problem with them but I can see how somebody else may have a different opinion. They're better than Drake's 3.5mm boots (Drake 800g Thinsulate vs. MPW 1,000g). If your feet get cold and you don't do a lot of walking, the 5mm may work better for you, but if you've got a long walk you're going to burn up in the 5mm's.