Why Does Car Glass Fog Up?

[VanReed]

Car glass fogs up due to high humidity and low temperature, both conditions being necessary. Below are the relevant explanations: 1. Humidity Reason: When the air humidity is constant and the window temperature falls below the dew point, condensation forms on the window surface, which is commonly seen as fogging on the windshield. 2. Temperature Reason: When there is a certain temperature difference on both sides of the window, and the saturated vapor pressure of water on the colder surface is lower than the surrounding environment's vapor pressure, moisture gathers on the glass surface, appearing as tiny water droplets, thus forming fog.