Why Do Car Windows Fog Up From the Inside? | RapidSmartFacts

Driving on a damp day? Your windshield suddenly fogs up inside. Why does fog

form on the inside, not outside? Fog on glass is just tiny

water droplets. These droplets form when humid air hits a cooler surface.

Inside the car, you create humidity: breathing, damp clothes, wet shoes.

When moist air touches the cold window, it quickly cools. Cooler air cannot

hold as much water vapor. The extra water then condenses into tiny droplets on

the inside. That’s why turning on the defroster and fan helps. Warm,

dry air from vents heats the glass and dries the cabin. Using A/C,