What Causes Persistent Fogging on the Windshield?

[McArthur]

Window fogging is primarily caused by temperature differences. Temperature Difference: Due to the temperature disparity between the interior and exterior of the vehicle, windows are prone to fogging. This occurs because the window glass, being in contact with the outside environment, remains cooler, causing the water vapor inside the car to condense on the glass and form fog. When the window temperature is below the dew point at a certain air humidity level, condensation readily forms on the window surface, leading to the common fogging phenomenon on the windshield. Principle: If the temperatures on either side of the window differ, the surface with the lower temperature will have a lower saturation vapor pressure than the surrounding environment. This causes water vapor to accumulate on the glass surface, emerging as tiny water droplets that create fog.