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

On a cool, damp day, your car's windshield suddenly turns cloudy inside.

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 clear it. Warm, dry air from the vents heats