Family Road Trip - How to Stop Car Windows Fogging Up 

How to Stop Car Windows Fogging Up 

While driving down the highway and your car window fogs up, the first thing you do is blast the defroster. The fog clears but then builds up a few minutes later. 

The same thing happens to the car driver and passenger side windows. The windows fog up, hindering you from seeing your rearview mirrors. You roll your car windows down and back up to eliminate the moisture. But then the fog comes back again. 

And you are left wondering how to stop car windows from fogging up completely. Fortunately, there are ways to escape this seemingly endless cycle of fog recurrence and achieve nirvana. 

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What Causes Fogged-Up Car Windows 

Moist, warm air condensing when it hits your car’s colder windshield causes condensation. The air next to the window below a specific temperature is called the dew point.  

Many reasons, like humidity (inside and outside the car), temperature variations, and chilly weather, could lead to foggy windows. 


Humidity (water in the air) causes a buildup in water that turns into water vapor. When you get inside your car, you breathe the humid air. This air comes out from inside your body or off of it. 

Car fogging up inside tends to be more of a problem when there is more than one person in the car since there will be more breathing.  

Surface Tension 

Surface tension is another reason that causes the inside of your car window to fog up. This is because water molecules choose other water molecules to form tiny droplets of water. These droplets will attach to your car windows and cause fog. 


In the early mornings, moist warm air will condense when it hits your car’s colder windshield. This is why condensation forms at the windshield base, which meets the cool air when your air conditioning runs on those humid, warm days. 

You’ll also notice that on cold mornings when you turn on the heater in your car, fog will start forming on your windows. This happens because water needs to find its way out someplace. You’ll notice that on such cold mornings, fog or dew is on the ground because the warm, moist air contacts the ground. This same thing happens to your car when it’s warm inside and cold outside.  

Family Road Trip - Foggy Car Windows


Temperature is the action of molecules in motion. Warm air holds more moisture than cold air. This doesn’t mean that molecules are holding onto water molecules. When it’s warmer, more water turns into gas than it is liquid. This creates more space between each molecule with warm air, meaning water molecules thus can fit into this space between molecules.  

How to Quickly Clear Fogged-up Windows 

Understanding how windscreen fog is formed/ created can help you get rid of it depending on the season. Fog gathers on your car’s windshield when a temperature difference in the air meets.  

This means that fog in the summer is formed when your cool windshield hits the hot air outside. On the other hand, winter fog gathers when the warm air in your car meets your cold windshield. 

But whether the fog is inside or outside your car windows, it’s potentially dangerous as it hinders you from having a clear view of all directions. Here is how to ensure that your car windows are clear- no matter the season or weather. 

When the outside is colder than inside your car: 

  • Change your air source 

With today’s technology, most cars come equipped with buttons that will allow you to recirculate the air in your car or pull air in from the outside. If you are starting to see fogged-up car windows, you should change the settings so that the air gets pulled up from outside.  

There is probably a button with a little car drawn and an arrow pointing inside the car. Tap this button so that the light above it is on.  

Alternatively, you can tap the button with a car and a circular arrow inside so the light goes off. By so doing, you will be turning off the function that recirculates the air already inside your car. 

  • Lower the temperature in your car 

As earlier stated, car windscreen steaming up is caused by the temperature difference; therefore, getting the air temps inside your car to match the air outside will reduce fog. 

Turn your car fans on to the highest setting and turn the air temps down as cold as possible. But be prepared to shiver a bit, as this is the fastest but coldest method. 

Family Road Trip - Car AC Temperature
  • Turn on the defrost vent on with cool air: 

Your car’s defrost vent will direct air straight at your windshield, but the cool air will help your windshield temperature to match the air temperatures outside. This will help get rid of fog on your windshield. 

When it is warmer outside than in your car: 

When the temps and moisture level outside are great compared to the inside of the car, moisture will condense on the exterior of your car glass. Your goals are to change the temperature inside the car to match the outside temperature. 

  • Turn down the AC if it is warmer outside: 

If you got water vapor on your car windows during the summer, turn down your air conditioner. Turning down the air conditioner will warm your car and get the inside air temperature to match the outside better.  

You can also opt to open your windows a bit to allow more outside air in, preventing your car from becoming too stifling. 

  • Turn on your windshield wipers: 

Mostly the fog will form outside of your windshield during the summer. This means that you can be able to remove it with your windshield wipers. Turn the windshield wipers on to their lowest setting and allow them to run until the fog is all cleared up. 

  • Open your car windows: 

Opening your car windows is a quick way to get the temperatures inside to match the outside temperatures. Roll down your car windows as far as you can so that the warm air outside gets into the cool interior of your car. 

Driving with fogged-up car windows can be hazardous, but with the above tips, you can increase your safety while on the road. 

How to Prevent Fogged-Up Windows  

Having to deal with fog while in a rush can be frustrating. To prevent foggy windows in the future, try out these tips. 

Apply some shaving cream to your windshield: 

When buying shaving cream, look for the type that foams up when you squirt it out of the bottle or can. Spray a small portion of the shaving cream unto a soft cotton cloth and spread it over your entire windshield (ensure that you get every part). 

Then using a clean, dry rag, wipe it off. Doing this, you should create a moisture barrier on your car window, thus preventing fog buildup. 

Use silica cat litter

One way to limit moisture on your car windows is to ensure that it ends somewhere else. Fill up a sock with silica cat litter. Tie up the open side of the sock with a piece of string, and then place one or two full socks (packed with silica litter) near the front of your dashboard. 

Placing the socks with silica litter on the dashboard will help absorb the moisture inside your car during the night, preventing any fog buildup. 

Keep your car windows rolled down if possible

If your car is in a secure area, roll your windows down about half an inch. Rolling your windows down allows some outside air to get into the car and can prevent the windscreen from fogging. 

This method is best practiced during the summertime since you do not want to risk any snow or ice getting into your car during the winter

Keep your car clean

Fog needs to cling to something; therefore, the cleaner your windshield is, the less foggy it will be. Your windshield collects particles from the interior and the road outside, creating a film inside your windshield. 

Remember to clean your windshield from time to time. Also, never try to use your hands to wipe away the fog, as it only makes matters worse. 

Preheat your car 

Preheating your car with an interior heater is the most reliable way to prevent it from forming fog. Preheating ensures that everything inside the car has high enough temperatures from the get-go. Should you feel the air is humid, open the windows and doors for a few seconds to let it out. 

More Driving & Road Trip Preparation Advice

Whilst the weather can certainly make driving more challenging, there’s no reason without the right preparations steps you can’t continue to road trip year-round.

You may want to dig further into our driving and car care advice series, including:

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© Family Road Trip 2024

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