why do windows fog up

Windows fog up because warm, moist air meets a cooler surface, causing condensation. Basically, your windows become tiny dew collectors, much like a cold beer on a hot day. When the temperature of the glass drops below the dew point of the surrounding air, water vapor condenses into tiny droplets, creating that misty blur. Inside cars or homes, this often happens when humidity is high and ventilation is poor. So next time you see your windows fogging, blame it on physics, not your questionable housekeeping skills.