How to prevent the inside of your windshield from fogging or freezing

Fogging within a windshield occurs when vapor water from inside warm automobile condenses on the windshield cold. The air in the car absorbs moisture from the exhaled breathing of the passengers or any wet clothes they carry. If the heater is turned on, the air in the car heats up, allowing it to absorb more water vapor. When that moist air touches the cold windshield, it cools and becomes super-saturated, and the water vapor condenses. If the windshield is cold enough, condensation can become ice. This creates a potentially dangerous situation, because fogging or freezing on the windshield limits the driver’s visibility.

Instructions

1. Direct hot air to the windows using the defrost setting. As the windshield warms up, there is less temperature difference between the windshield and the air in the car, so condensation is less likely to occur.
2. Disables air recirculation control. Turning the air back on helps to quickly heat the car, but it also increases the humidity inside the car, passing the same air through again and again, absorbing more moisture from the occupants while doing so. Since cold air will withstand less moisture than warm air, air entering from outside will be less humid than warm air from inside, even if it rains or is snowing.
3. Turn on the air conditioning. The compressor removes moisture from the air inside the vehicle, so that the air striking the inside of the windshield is less likely to oversaturate.
4. Remove rain or snow before getting into the car. The extra water in the car increases the humidity, so do everything you can to limit the amount of water entering the car. Whenever possible, shake the umbrellas, coats and boots out of the car. Do not leave open liquid containers in the car. If the seats get wet, wipe the moisture off as soon as you can. Do not leave damp cloths or other items in the car.
5. Clean the windows with an ammonia-based or shampoo-based cleaner. There are also liquid treatments and commercially available towels that are specifically designed to deal with windshield fogging.