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

You’re driving on a cool, damp day and suddenly the inside of the windshield

gets cloudy. Why does the fog form on the inside, not outside?

Fog on glass is just tiny water droplets. Those droplets form when humid air

hits a cooler surface. Inside the car, you’re the source of humidity,

breathing, damp clothes, even wet shoes. When that moist air touches the

colder window, it cools down. Cooler air can’t hold as much water vapor.

The extra water condenses into droplets on the inside surface. That’s why turning

on the defroster and fan helps. Warm, dry air from the vents heats