What makes Thinsulate insulation so important to a cold-weather boot? Three words: thin, warm, light. Thinness, of course, is crucial in a boot insulation. There is simply no room for anything bulky. The same goes for warmth. Feet, being furthest from your body's center of heat, need insulation more than any other part of your body. With nearly twice the warmth of foam, felt or pile, Thinsulate insulation is just what feet need to stay warm and comfortable. Which brings up the third big benefit of Thinsulate insulation: It doesn't bog boots down with weight. In fact, it's one of the lightest synthetic insulations on the market.