..... The hood is the primary protection from frostbite for the face. If the hood has a proper tunnel (a deep one, mine is over 6" deep when forward) the air in front of your face is warmer that that outside, often LOTS warmer. The opening can also be closed down to a small circle. The ruff helps to keep the air in the hood from convecting. The big problem is that wind can blow away that warm air. The fur helps hold the still air and prevents wind from bouncing off the inside of the tunnel. If you don't have a ruff, you can only walk downwind. With a good ruff you can walk maybe as much as 45 degrees into a gentle wind. If the wind is strong the Inuit (and most others) will not travel. They find a sheltered spot (even a small depression), take off their mittens and sit on them. Back to the wind they pull their knees up inside their parka and wait out the wind. Some of the most patient people I have ever met. In northern villages a wind indicator is much more prized than a thermometer. The temp can be delt with but not the wind. ......

For a very interesting discussion try "Hunters of the Northern Ice" and "Paradise Below Zero". Both excellent descriptions of the old and very successful methods of enjoying extreme cold.