The beauty of these mittens is the fact that they are completely vapor permeable — a necessary feature required when you are operating in an extremely cold environment. As the moisture is coming out of the pores of your skin on your hands you simply do not want it to stay within the handwear. Also, time and time again, the 70 denier nylon taffeta has shown that it warms quickly to the temperature of your skin surface and, once equal to it, absorption of heat by the nylon stops. Due to the extraordinary ability of the continuous filament fiber to insulate, heat loss is minimized so your hands stay warm for extended time periods, which I put in the 'many hours' time frame. Based upon past knowledge of how well the original Antarctic mittens have performed for the past 20 years or longer I do not doubt these will perform equally as well.