Other than aggressive drivers and traffic jams, it’s hard to name something more annoying than figuring out how to defog windows during a long commute.
Window fog makes it hard to see the road ahead, and like a pesky bee to a soda can, it always comes back.
Fortunately, car experts have clearing foggy car windows down to a science. Keep reading for advice on how to defog windows and some tips for making it happen faster.
HOW TO DEFOG WINDOWS ON A COLD DAY
The fog that forms on a windshield is actually condensation created when water vapor in the air near the glass falls below or above a certain temperature, known as the dewpoint. When the temperature of a car cabin gets warmer than it is outside, that’s when the moisture from our breath and clothes condenses on the inside of the windshield and windows.
When the windshield gets foggy, the go-to move for many drivers (including myself) is to blast the defroster, using the hottest heat and strongest setting to clear the glass. The warm air from the defroster helps evaporate the moisture near the windshield, but it’s only a temporary fix.
If you want to stop the fog from forming, experts recommend using cool air to lower the temperature on the inside of the glass. You can accomplish this by blowing cool air out of the defroster, turning on the air conditioner (which acts as a dehumidifier) or by cracking the windows, if you can tolerate a brief face-full of cold air.
John Paul, AAA’s Car Doctor, recommends turning off your car’s “recirculate” button (shown above). When it’s off, the car pulls in dry air from outside the car to clear the windshield, instead of using moist air inside the car, which causes the problem in the first place.
“The other issue that causes moisture on the inside of the car is damp carpets,” Paul said. “It is always a good idea to wet-vac the car after a week of getting in and out of the car with snowy boots.”
HOW TO DEFOG WINDOWS ON A WARM DAY
Getting rid of fog on the outside of the windshield when you’re running the A/C in the spring is much easier—just use your wiper blades.
But if the humidity outside the car is causing the side windows to fog up, try using the opposite logic of what to do on a cold day. That is, use warm air, or the least-powerful cooling setting, to raise the temperature inside the cabin a little bit. That way you’re not putting the windows up and down every five minutes or turning the wiper blades off and on the entire trip.
OTHER TIPS AND TRICKS FOR FOGGY CAR WINDOWS
Cleaning the inside of your windshield will help prevent fog before it happens, said AAA spokesperson Cheryl Parker. Fog has a harder time forming on a clean surface, and an easier time forming on dirt and the film left behind from smoking, so he recommends taking a couple minutes over the weekend to spruce it up. Use a non-sudsing ammonia for the best clean, he said (just make sure to crack the windows open while you do it so you don’t inhale the stuff).
Another, more unusual tip, comes from YouTuber DaveHax, who recommends keeping a sock full of kitty litter on or close to the dashboard. The litter is very absorbent, and can help contain some of the moisture in the cabin.
Also, keep wet belongings like a recently used umbrella or sweaty gym clothes in the trunk if you want to cut down on the amount of moisture inside your car (hey, every little bit helps).
WHAT NOT TO DO
Lastly, most people know this, but it bears repeating: Avoid wiping foggy car windows with your hands. Hands carry oils that will transfer to the glass, so while it could temporarily defog car windows, it might just make the problem worse later on. Keep a microfiber cloth inside your vehicle in case you have to clear the windshield in a pinch.
And when you clean your windshield, avoid spraying a cleaning product directly on it—where it will splash on the dashboard and elsewhere. Spray your solution on a microfiber towel, and wipe up and down, and side to side, using long strokes. Then use another towel to wipe off any excess spray.
Now that you know how to defog windows, you’ll know what to do the next time things get steamy inside your car.