What Causes Fogging on Car Windows in Rainy Weather?
2 Answers
Fogging on side windows during rainy weather can be addressed using toothpaste, water repellent, or air conditioning defogging. Below are specific solutions for fogging: On rainy days, evenly apply toothpaste or soap to the car's side windows and let it sit for a while until the applied soap hardens. Then, wipe it clean with a towel. This will form a wax layer on the glass surface, which has excellent water-repellent properties and can effectively prevent fogging or water droplets on the rearview mirror, ensuring clear visibility. Purchase a specialized water repellent and evenly spray or apply it to the rearview mirror. The rearview mirror surface will form a protective film, which also has excellent hydrophobic properties, effectively preventing fogging or water droplets and ensuring a clear rearview mirror. Turn on the car's air conditioning to cold air and adjust the vents to blow toward the front windshield to quickly clear fogging. For a more thorough solution, turn on the air conditioning to hot air before starting the car and blow it directly at the front windshield for 3 minutes. This can fundamentally prevent glass fogging. Air conditioning cooling can also dehumidify and achieve the fastest defogging effect. The driver can turn on the air conditioning's cooling mode and adjust the air flow to the windshield setting. The fog should disappear in about ten seconds.
I've been driving big trucks for long hauls for over 30 years, and foggy windows on rainy days are all too familiar—it's all caused by temperature differences. On rainy days, the cold wind and rain outside chill the windows, while we sit warm inside exhaling moist air that condenses into fog when it hits the cold glass. Turning on the heater or AC makes it worse, as warm air carries more moisture, thickening the fog. I still remember nearly hitting a tree in the mountains last year because the fog blocked my vision—it was terrifying. Now, as soon as I get in the truck, I switch the AC to external circulation, directing the airflow at the windows to dehumidify and turning up the temperature to speed up water droplet evaporation. I also keep an anti-fog spray handy and apply it regularly. Don’t get lazy when driving in the rain—safety comes first. Everyone should practice defogging techniques beforehand, not just when trouble strikes.
