Anyone who's been outside on a windy, winter day knows it's a lot more difficult to stay warm than on a calm day with the same temperature.

　　On a calm winter day, our bodies warm up a thin layer of air close to our skin -- called the boundary layer -- and that helps to insulate us from the cold air. However, when the wind starts to blow, it strips away this boundary layer and our skin is more exposed to the cold air.

　　Because wind chill speeds up the rate at which your body loses heat, it can be dangerous. Each year in Canada, more than 80 people die from overexposure to the cold.