Why Do Windows Fog Up And What You Can Do?

In recent times, given the rainy seasons and cooler temperatures – some if not most of us might have experienced condensation or fogging of our windows and windscreens.  A fogged-up windscreen or window reduces the visibility of the outside, which makes it a hazard when driving.

So in this report, we hope to shed some light on why your car windows fog up, and what you can do to prevent it from happening.

Your car windows fog up because of a physical process call condensation.

What is condensation?

Condensation forms when warm air containing moisture comes into contact with a cold surface, such as your car window. When the warm air meets the cold air, the moisture in that warm air condenses onto that cold surface.

On a car windscreen or window, this moisture takes the form of hundreds of tiny (microscopic) water droplets that, from a driver’s perspective, will look like a blurry fog.

What causes condensation inside a vehicle?

In Malaysia, condensation inside your car mostly happens when the interior temperature is warmer than the colder temperature outside (such as when it rains) – causing the windscreen/window to become cold.

One or a number of the following things could cause condensation inside the car:

• Wet clothes/shoes/spilled drinks – moisture from these items will slowly evaporate into the cabin air or, if heavily soaked, cause the seats and carpet to become wet.
• A water leak – this is mostly caused by leaking body seals.
• Breath – this is less of an issue in Malaysia, but exhaled air contains a large amount of water vapour which is released into the cabin.
• No circulation of fresh air – such as when your car is parked for long periods.

Modern cars have much better seals (between the doors and body, and between the windows), meaning they tend to be more watertight. However, this also means that it’s more difficult for any air inside the vehicle to get out. Increased insulation also allows modern cars to stay warmer/cooler longer after being parked; the longer the air inside the vehicle is warmer than the air outside, the more condensation will appear on the cold windows of the vehicle.

As condensation collects in the air inside the cabin, the level of moisture will increase. If this air is not vented to the outside then more condensation will build upon the window surfaces.

What do I do when my windows are fogged up?

The most efficient way to remove moisture from the air is to use the vehicle’s air conditioning system. This system draws air from the cabin through an evaporator, which causes moisture in the air to condensate in a controlled way and drain out of the vehicle.

If the cabin air is not regularly refreshed then condensation will accumulate, as the moisture-filled air will not be removed. However, you can force this by changing the re-circulation feature from internal to fresh air.

You can also use the demister function which is designed to clear the windscreen of condensation. This works by directing fresh air onto the windscreen, which has the effect of drying the inside of the glass.

Believe it or not, one of the easiest ways to keep condensation at bay is by simply keeping the insides of windows, particularly the windscreen, as clean as possible. You can do this by using a good glass cleaner and wiping window surfaces thoroughly dry with a paper towel or old newspaper.

A thorough clean of the windscreen will lessen the likelihood of condensation forming and ensures that any that does form is removed quicker by the demisters.

Is there anything else I can do?

Well yes, there are a number of things you can use (even household items) that can reduce the effects of fogging in your vehicle, here are some examples:

• Car dehumidifier bag: This is a small bean bag full of silicone balls that sits on the top of your dashboard and soaks up moisture from the air inside your car at all times
• Anti-Fog Glass cleaner/protectant: There are several anti-fog glass cleaners on the market. Simply spray onto the glass surface and wipe dry with a microfiber towel.

And a few household item hacks:

• Shaving cream: shaving foam contains surfactants which once applied, leave behind a protective coating which prevents condensation.
• Toothpaste: toothpaste contains chemicals, which like shaving cream, leave a protective coating on the glass surface. We advise to use sparingly and with caution as toothpaste’s other cleaning compounds can also scour the glass surface. 
• Kitty litter – “Unused” of course, but kitty litter is also made from Silica-based chemicals like dehumidifier bags, simply place a scoop in an old sock (or the like) and place it near the glass surface to prevent fogging.