Why is there frost on the car's interior windows?

[BriellaDella]

The reason for frost forming on the interior windows of a car is: After people leave the car at night, residual heat remains inside the vehicle, causing the temperature of the windows to be higher than the outside. If the external temperature is too low or it's snowing, the moisture inside the car will solidify into ice beads, forming frost on the windows. Here are some methods to remove frost from car windows: 1. When parking after using the car, don't immediately lock and leave. Instead, wait patiently for a while, open both doors to ventilate, and wait until the interior temperature drops to nearly match the outside temperature. Then, turn on the power and use the windshield wipers to clean any remaining snow or water from the front windshield before leaving. 2. Frost on the rear window is easier to handle. Most cars are equipped with a rear window grid-style defroster. The defroster consumes battery power when operating, so always start the engine first before pressing the rear window defogger switch. The defroster will automatically turn off after 10 minutes.

[MacSara]

The most annoying thing about driving in winter is getting into the car only to find the windows covered in a thick layer of frost, making you shiver from the cold. This usually happens because there’s too much moisture inside the car, and when temperatures drop at night, the moisture condenses into frost on the windows. Every day, I drive my kids to and from school—the car is packed with backpacks, snow-soaked umbrellas, and a few warm little kids exhaling moist air. The next morning, the windows are guaranteed to be frosted over. I have to turn on the heater five minutes early, blast the defroster mode with the fan at max, wait for the frost to melt into droplets, and then wipe it dry with a cloth. Before parking, I also have to leave the windows slightly cracked for ventilation, or I’ll definitely regret it the next day.

[StKatherine]

Last time during heavy snowfall, I almost arrived late due to frost on the car windows, but later I figured out the principle. The moisture from human breath freezes into frost on the cold glass, especially when the car is tightly sealed, making the frost thicker. I now cover the front windshield with newspaper before bedtime, which keeps it warm and absorbs moisture. In the morning, I start the car, turn on the external circulation and defrost button—cold air removes frost faster than hot air. I always keep a defogging spray handy; one application lasts several days. If wet clothes or umbrellas are left in the car, frost forms faster, so timely cleanup is crucial.

[SanWyatt]

Rushing to work early in the morning to meet clients, only to find frosted windows is truly frustrating. The core issue lies in temperature difference and humidity—when the outside is below freezing, the residual warm, moist air inside the car hits the cold glass and instantly frosts over. My habit is to roll down the windows for half a minute to ventilate before parking, then wipe the inside of the glass with a dry cloth. If the frost has already formed in sheets, don’t scrape it hard—just turn on the AUTO mode of the air conditioning, and it will start melting in 20 seconds. Insufficient antifreeze can also weaken the heating effect, making regular checks essential.

[VonOwen]

As a veteran driver with ten years of experience, the key to defrosting lies in prevention. Surprisingly, placing a bag of cat litter in the car as a desiccant works wonders by absorbing excess moisture. The main culprit of frost is often running the air conditioning on recirculate mode for too long, trapping humidity inside the car. Now in winter, I always use the fresh air mode, directing warm air towards the windshield and footwell. Remember to clean the cabin air filter weekly—a dirty filter drastically reduces dehumidification efficiency. Before parking, turn off the heater and open doors to vent steam for five minutes, ensuring crystal-clear windows the next morning.