Today I watched a glass of ice water "sweat" on the kitchen counter and reminded myself that condensation isn't the water leaking through the glass. It's water vapor from the air turning liquid on the cold surface. I used to think humid air was "heavier" because it felt thick, but water vapor is actually lighter than dry air—individual H₂O molecules weigh less than N₂ or O₂. The confusion comes from the fact that humid air often coincides with low-pressure systems and still conditions, which make the air feel dense.
I ran a tiny experiment: I filled two identical glasses with ice water, then wrapped one in a dry towel. After twenty minutes the bare glass was dripping, the wrapped one bone-dry. The towel insulated the surface, keeping it above the dew point. It's a reminder that condensation needs a cool surface
and