What Causes Fogging Inside Car Windows?
2 Answers
The reason for fogging inside car windows is the temperature difference between the warm interior and cold exterior, typically around 10-20 degrees Celsius. When carbon dioxide exhaled by passengers inside the car meets the cold glass, it condenses into water vapor, forming fog on the windows. Methods to defog car windows include: 1. Opening windows slightly to allow air circulation, suitable when fogging is not severe; 2. Creating airflow by driving with windows open to reduce the temperature difference and eliminate fog; 3. Pressing the front windshield defogger button on the central control panel and adjusting the air vents to direct airflow toward the windshield; 4. Evenly spraying defogging solution onto a soft cloth and wiping the windshield, or applying it directly to the glass.
Every autumn and winter, driving becomes a headache due to foggy windows, which is actually caused by differences in temperature and humidity inside and outside the car. The warm air exhaled by passengers condenses into tiny water droplets when it hits the cold glass, especially noticeable on rainy days. A few times, I noticed that opening the window immediately clears the fog—turns out, the collision of warm and cold air quickly eliminates the temperature difference. However, opening windows on the highway isn’t practical, so you have to rely on the air conditioning system—switch to the defrost mode and turn on the AC for dehumidification. Both warm and cold air work, but cold air is faster. Nowadays, many new cars come with a dedicated defogging button, which is really convenient. Additionally, humidity inside the car also plays a role—remember not to leave wet umbrellas or clothes on the back seat right after washing the car. Developing a habit of turning off the heater before parking to let the glass temperature rise can effectively prevent fogging the next day.
