What to do in case of fogged glass

With autumn and the drop in temperatures, one of the small daily annoyances for those who drive returns: fogged windows. This phenomenon, caused by condensation, occurs when the warm, humid air inside the cabin due to our breath or the heater meets the cold glass. In this article, we’ll explain how to quickly get rid of the problem every time you get in your car and how to avoid putting yourself or other drivers at risk.

How to defog car windows

To understand how to defog your car windows, you first need to determine whether the fogging is on the inside or outside. Internal fogging is the most common: it forms because the air inside is more humid than the air outside. The best solution is to turn on the air conditioner, even in winter, and direct the airflow toward the windshield. The A/C dehumidifies the air before heating it, removing moisture and clearing the glass more quickly.

External fogging is rarer and usually occurs when the outside air is very humid but warmer than the glass surface. In this case, simply turn on the windshield wipers or, if necessary, direct warm air at the glass without turning on the A/C.

Another common question about how to defog car windows is: hot or cold air which works better? Scientifically, cool, dehumidified air (the kind produced when the A/C is on) is most effective because it quickly reduces the humidity of the air in contact with the glass. However, immediately afterward, it’s advisable to switch to warm air (still with the A/C on) to raise the glass temperature and prevent new condensation from forming. In summary, the winning combination is: air conditioning to dehumidify + warm air to heat the glass.

To prevent condensation, you can follow these simple tips:

1. Turn off air recirculation and use outside air, which is usually less humid than the air inside the car;
2. Regularly clean the inside of your windshield condensation adheres more easily to dirty surfaces;
3. Use specific sprays or microfiber cloths to treat interior glass surfaces.

Driving with a fogged windshield: what are the risks?

Driving with a fogged windshield or windows is not only dangerous but also punishable by law. The Highway Code is clear: the driver must always maintain perfect visibility of the road and surrounding environment.

Article 152 of the Highway Code (regarding the field of vision and visibility of the license plate) and Article 140 (on the general principle of caution) are often used by law enforcement to cite unsafe driving due to fogged windows. In fact, a fogged windshield drastically reduces the field of vision especially at the sides and in low-light conditions increasing reaction time in an emergency.

If an officer determines that fogging prevents the driver from having a clear and complete view, thereby endangering road safety, an administrative fine may be issued. The amount can vary, but the citation generally concerns the violation of prudence and diligence while driving.

To avoid risks and fines, it’s essential to always wait until the windshield is completely clear before setting off. Your safety and that of other road users comes before any delay!