How to Defog Your Windshield, According to a Former NASA Engineer

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Why is there frost on the inside of my house windows?

Frost forms on windows when they are exposed to cold air on the outside, moist air on the inside. Moisture in the room’s air (water vapor) is drawn to the window pane, and when the outside surface temperature lowers past the dew point, that water vapor solidifies into liquid. Frost can cause damage.

Can you put cold water on frozen windshield?

Heating up the windshield with warm water would melt the thin layer of ice. All you’d need to do is turn on the windshield wipers to wash away the remaining water. But it’s more dangerous than it sounds. A rapid change of temperature, caused by pouring hot water on a frozen surface, can cause the glass to crack.

DIY anti fog winshield

Rubbing the windshield glass with your hands can help remove condensation but only momentarily, so it’s not the best way to defog your car.

We recommend soaking your windscreen with a mixture of soap and water before starting to circulate. After passing a dry cloth over the windshield, remove the soapy solution well. This DIY trick will help avoid your car from fogging up too quickly.

How to Defog Car Windows

During the winter season or perhaps when you are driving in icy rain, you'll notice fog the windows. Often in bigger cars, say a Chevy Suburban, this happens at the front of the vehicle where the passengers are sitting, and smaller vehicles like hatchbacks often fog up quicker all around. The best way to clear these foggy car windows is with a steady supply of dry, hot air. Activate your car's air conditioning and turn up the heat, once the temperature from the AC has increased, select the windscreen vents, and watch the magic happen. Cold, fresh air will actually have the same effect, so if you don't have a working AC, crack a window and set your vents to circulate air from the outside instead of recirculating cabin air, this will diminish the humidity within the cabin and clear up the windows.

Wiping the windows down with a dry cloth or your sleeve isn't very effective as you'll likely just gather the moisture that's there and spread it around. Plus, because the temperature in the car wouldn't have changed, the condensation will just reoccur. Your breathing will also simply counter the efforts.

How to Defog Your Windows When It’s Hot

While less problematic for auto glass than cold wi

While less problematic for auto glass than cold winters, summer’s hot air and humidity may also fog up your windows. Unlike in the winter, summer fogging will occur on the outside of the glass, where the season’s warm, moist air condenses on AC-chilled windows. You can use your windshield wipers to clear fog on the outside of the windshield as an immediate, temporary measure to restore visibility. However, the key to preventing the fog is to allow the windows to remain warm. Redirect your car’s vents away from the glass, don’t use the defrost setting, and consider turning up the interior temperature slightly.

Do you use hot or cold air to defog a car windshield?

You should only use hot air to help evaporate the moisture from near your windshield, but this is a temporary fix. To prevent fog, use cool air to lower the temperature on the inside of the car glass.

Pro Tip: Keep Your Windshield Clean

You can take a few steps to reduce fogging and mak

You can take a few steps to reduce fogging and make it easier to defog a window if it appears. First, keep your windows clean—especially the inside of the glass. Even a slight haze from dirt can affect visibility in certain conditions. When you combine that dirt with fog, things can get dangerous.

Plus, a dirty window is more likely to fog up than a clean window. The tiny dirt particles are ideal areas for water to begin to condense, causing fog to occur more quickly and more often than it would on a very clean window. Regularly using window cleaner can help prevent fog from forming in the first place.

There are also specialized automotive anti-fog treatments, like Rain-X, that you can use on your windows. In combination with a clean window, these materials work well to stop fogging by reducing your windows’ surface tension and dispersing the fog’s micro water droplets into a thin water film that is much more transparent. Most products come in a liquid form, which you apply to a clean, dry window and polish to an invisible film.

Dealing With Foggy Windshield Inside And Outside Of Your Vehicle

Foggy car windows and windshield will be something you have to deal with as a car owner. This is whether it is more cold outside than in the car, or it is warmer outside than in your car.

You need to make sure that your windshield is free from fogging and hence clear enough when you are driving.

The last thing any driver want is to have their vision of the road they are driving on impaired by either too much fog or dirt particles.

Wipers might help but they would not be effective for cleaning the inner surface of the windshield.

The following is a detailed discussion about how to deal with a foggy windshield during different scenarios.

The steps here basically try to balance the temperature on the inside and outside so that both of them match.

1. If It’s Colder Outside Than Inside Your Car

During a cold weather, such as the winter, you may want to turn the heat up using the AC. This leads to fog forming on the windshield on the inside.

You can defog your windshield effectively and fast enough through:

  • Turn the heat to the point of maximum setting, simply because hotter air holds more moisture.
  • Turn the AC on, this pulls away the moisture from the air as it passes above the coils.
  • Switch off the recirculation button which will let in cooler and air with less moisture in the car.
  • Open your windows a little bit so that the humid air escapes and dryer air enters.
  • Otherwise, if your car has a defrosting button, you can hit it. This will blow warm air across the surface of the windshield on the inside and evaporate moisture that forms on its surface and impairs the vision through it.

2. If It’s Warmer Outside Than Inside Your Car

For this particular situation, the fogging would occur on the outer surface of the windshield.

The windshield wipers would not be able to clear this and at sometimes you are not in a position to walk out of the car wand wipe the surface of the windshield with a cloth.

Unlike when it was colder outside the car, here you will need to make the inside warmer:

  • Switch on the windshield wipers and let them work before you are able to achieve a balance in the inside and outside temperature.
  • Turn down the car AC so that it is at its lowest setting and let the temperature rise while it is comfortable to be in the car.
  • Switch off the car’s recirculation option which will ensure that the temperature and moisture levels between the inside and outside of the car is able to achieve a balanced level.

How to Defog Windshield when outside is warm?

To defog the windshield when outside is warm, you need to:

  • Use windshield wipers.
  • Set air condition on low or turn off air condition—warm-up car.
  • Turn off the recirculation button (30 seconds)


This occurs when the outside temperature and moisture level are higher than those found inside a vehicle. Changing the temperature in your car to match the outside temperature is similar to changing the temperature in your car when it’s colder outside than it is inside.

In this case, it means warming up the inside. Keep the following tips in mind:

Start by using your windshield wipers to keep your windshield clean. The condensation will be removed as a result of this action until the temperature is balanced. If this doesn’t work, Car manual recommends turning off the air conditioner completely.

Recirculation should be turned off: The recirculation feature of your car should be turned off to combat foggy windows. This will allow the temperature and moisture levels inside your car to match that outside.