The only thing about the mitten theory that's a bit off is if the wind is blowing. Cold plus wind equals chill factor. It can be 10 above zero but when you add in the wind it can effect the skin as if it were -10 or colder. When the temperature is below 30F I'm wearing heavy jeans outside. Having been frostbitten on several occasions I refuse to take the chance of a repeat if I can help it. Once you've had frostbite you become much more sensative to cold and more easily frostbitten again.