Why is there a layer of white haze on the car glass?
2 Answers
There are several reasons for fogging: 1. Reason one: When the air humidity is constant and the window temperature is below the dew point, condensation forms on the surface of the window, which is the fogging phenomenon we often see on the windshield. 2. Reason two: 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, water vapor gathers on the glass surface, forming tiny water droplets that seep out and create fog. If the dew point is above zero degrees Celsius, it results in fogging; if the dew point is below zero degrees Celsius, it turns into frost.
When I first started driving, I often encountered foggy windows, especially on winter mornings or rainy days when a layer of white mist would form on the windshield after starting the car, making visibility dangerously blurry. This is mainly due to high humidity inside the car condensing on the cold glass—such as moisture from our breath, wet clothes, or running the AC without the A/C button engaged, which can accumulate moisture. The solution is to immediately turn on the fan in windshield defrost mode, set the temperature to warm, press the A/C button to dehumidify, and ensure the ventilation mode is set to external circulation to draw in dry air. If there’s grease or dirt on the inside, simply wipe it carefully with a microfiber cloth dipped in glass cleaner. For prevention, I’m used to keeping a dehumidifier bag in the car, regularly replacing the cabin air filter to avoid clogging, and applying an anti-fog spray before driving for long-lasting protection—avoid keeping windows open too long in enclosed spaces. In short, don’t overlook this small issue; driving safety comes first.
