# Why does mist on glasses disappear when you go back outside in freezing weather?

This evening after a walk in the cold weather, about -5 degree Celsius, my glasses were misting up when I got back into the warm house, about +20 degree Celsius.

However, shortly after I went outside in the cold again, and the mist on my glasses disappeared. This puzzles me, since I guess the outside air to have nearly 100% relative humidity, since it is cooling down in the evening.

How come that the mist on my glasses can disappear in the freezing weather?

The $$absolute$$ humidity is much lower outside. The lenses of your glasses have some thermal inertia, and while you were outside they got pretty cold. When you step inside, where the absolute humidity is higher, a thin layer of air near the lenses cools to below the dew point, and condensation occurs.