How To Prevent Car Windows From Fogging Up


If you’ve ever tried to hit the road in anything other than perfect weather conditions, there’s a good chance you’ve dealt with your car windows fogging up. Few things are more annoying than trying to clear a plate-size patch of windshield when you’re already running late for work.

In this article, we’ll explain why windshields fog up in the first place. Then, we’ll ways you can use to quickly get rid of that pesky fog. Finally, we’ll talk about how to prevent car windows from fogging up in the first place.

What causes car windows to fog up?

In short, we can thank good old-fashioned science for foggy windows in the morning. More specifically, we can thank climatology. Your car’s windows fog up whenever the relative humidity point is lower, and that happens when the air outside your vehicle is colder than the air inside. Your car’s glass is a barrier, and condensation will form on this barrier when there’s too much water present in the air.

That excess water can be introduced in any number of ways. The most common source of moisture is your own breath (which, incidentally, you can’t do much about). Some other fairly common sources of moisture that can contribute to foggy windows are wet clothes (as a result of rain or snow), equally wet shoes or boots, and even steamy take-out dinner.

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In short, regardless of the source of the excess moisture, when it makes content with the cold windshield, you get instant fog.

How to get rid of foggy windows

How To Prevent Car Windows From Fogging Up

The good news is that you don’t have to resort to vigorously rubbing your windshield with that greasy Starbucks napkin in an effort to clear a peephole big enough to allow you to see to drive (or worse yet, attempt to squint through the foggy haze, which is dangerous, so don’t do it). Here are a few ways to clear your windows quickly if they fog up.

Don’t use that greasy napkin

As we mentioned above, your first reaction might be to wipe those foggy windows with the first item you come across, and often that item will be a used napkin or your gloved hand. When you do this, you’re leaving a film of dirt and oil on the glass, which actually makes it easier for moisture to stick to it. Chances are you’ve done this before, and you probably noticed that the glass simply fogs up again within seconds of your clearing a spot.

Crank up the heat

Your first step to successfully defogging your windshield is to blast the heat in your vehicle. Crank it up to its hottest setting. We know it sounds counterintuitive, but what you’re doing here is actually introducing more moisture into the air inside your vehicle. Hot air holds more moisture, so let it rip.

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Crank up the A/C

We know—when it’s freezing outside it might sound ridiculous to blast your air conditioning, but trust us, it’s a vital step in defogging your car’s windshield. When you crank your air conditioning, it will help pull the moisture out of the air inside your vehicle thanks to your AC’s cooling coils.

Turn off the recirculation function

Another key to defogging your car’s windows is to replace the warm, moist air inside with the cooler, dryer air outside. To ensure this happens quickly, make sure you turn off the recirculation function on your AC’s system.

Open your windows slightly

Finally, as you’re running through all of these steps, crack your windows a bit to help all that warm, moisture-filled air escape. Once you’ve cleared away the fog, keep your defroster on while you’re driving to help keep your windows from defogging.

How to prevent windows from fogging

As is the case with most vehicle issues, the best way to “fix” foggy windows is to prevent it from happening in the first place. That’s easier said than done, but we have a few tips to help. While these tips won’t completely prevent fogging in all situations, they will—at the very least—make clearing your windows much easier.

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De-ice the outside of your windows

As we’ve already mentioned, the main reason your windshield fogs up is because it’s much colder than the air inside your vehicle. As you might imagine, when you have a buildup of snow or ice on the outside of your windshield, it can be pretty difficult to lower the temperature!

Keep a bottle of quality deicer in your vehicle, and give your windshield a good spray on the outside before trying to start your car and defog the inside. One of our favorite deicers is the Prestone Windshield Deicer. It quickly melts ice and snow, and what’s more, it won’t ruin your clothing if you get some overspray on you.

If you know you’ve got some snow coming, consider throwing a sunshade on your windshield before the storm hits. Even cardboard works in a pinch. You won’t have near as much snow to clear away when you head out for work the next morning.

Minimize the moisture inside your vehicle

Other than temperature, the other biggest factor in foggy car windows is the moisture inside your vehicle. As much as you’re able, try to keep your shoes and clothing dry before entering your car. That means using an umbrella and knocking excess snow off your shoes before you put them on your carpet.

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If your vehicle constantly feels damp, check your floormats for water. You may have a leak in your door seals or the windshield itself if they’re wet. If you have a crack in your windshield, you’re almost certainly getting some amount of water inside your vehicle, and that’s going to make defogging a real pain. Consider replacing your windshield.

Keep your windows clean

As we mentioned, if your windows get a buildup of dirt and grease, moisture is going to stick to them and your fogging issue will be more severe. Routinely clean your windows with a quality glass cleaner. We also recommend using a Rain-X product on the outside of your windshield. It will help create a protective film that will not only help keep your windshield clean but will also make you a safer driver in the rain, snow, or ice.

Give yourself plenty of time

If you know you need to hit the road and you’re going to have to defog your windows, make sure to give yourself plenty of time to prep your vehicle. Your engine will need to warm up before you can effectively get all of that warm, moist air out, so try to head out to your car and get everything going 10 or 15 minutes before you need to hit the road. That should be enough time to defog your windows and you won’t be tempted to drive with an unsafe degree of visibility.

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Crack those windows

If you’ve just jogged through a downpour of rain or snow to get to your vehicle and your windows haven’t fogged up yet, there’s a good chance they will once you’ve gotten down the road a bit. To help get all of that moisture you introduced out of your car in a hurry, don’t be afraid to drive a bit with your windows cracked. Sure, it might be a bit chilly, but a few minutes of shivering is much safer than hitting the interstate with foggy windows.

Final Thoughts

Foggy windows are more than just a pain in your morning commute. They’re a serious safety hazard. The tips outlined above have hopefully given you some insight into the science behind why your windows fog up in the first place, as well as some ways to defog them and minimize future occurrences.

However, your most useful tool in safely hitting the road when you have foggy windows is time. Give yourself plenty of time to defog your windows and never try to hit the road when you can’t safely see. Wnat to learn more tips for successfully preparing your vehicle for cold weather driving, check out this article.

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