How to stop condensation on car windows: what causes inside of window to steam up and tips to clear quickly

Advice on why car windows steam up, the quickest way to defog them and how to stop it happening

Police in Scotland recently shared a photo of a car whose driver had just been fined £100 and given three penalty points for driving with a fogged-up window.

The image showed a ridiculously small patch of clear glass surrounded by thick condensation and came with a warning that driving a car in such a condition was dangerous and illegal.

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Condesation on car windows is a regular problem at this time of year. Often it’s an issue first thing in the morning as you’re starting your journey but can occur at any time, depending on the conditions, so it’s worth knowing what causes condensation, how to clear it and how to prevent condensation forming in the first place.

Why do car windows fog up?

The condensation or “mist” on your car windows is formed when warm moist air inside the car comes into contact with the cold glass surface, which is why it’s such a problem during winter. The heat from your body and breath warms the air inside the car and increases the moisture levels. When this air then comes into contact with the cold glass, it condenses and causes the mist or fog on the windscreen and windows.

The best way to demist your windscreen

The quickest way to clear condensation from your windows is to use a clean cloth or demisting pad. However, this can leave streaks on the glass and is a short-term solution that won’t stop it forming again quickly, so you are better to use your car’s ventialtion system.

Start by ensuring all the vents are directing air towards the windscreen and windows then turn the fan up full. Keep the temperature low to begin with as setting the temperature too high will just create more moist air and problem. The cold air from the fans will still be warmer than the glass and help dry it out, at which point you can then turn up the heat.

Activate your car’s air conditioning, if it has it. This will help to dry the air out more quickly.

Don’t use recirculation. This will warm the car quicker but keeps the moisture trapped inside.

Open the window. Especially if you don’t have air conditioning, this will help clear the screen faster by drawing in cold dry air from outside, which will help reduce the moisture inside.

How to stop condensation forming on car windows

Easier than clearing your glass is taking the following simple steps to reduce the chances of condensation forming in the first place.

  • Clean your windows - removing tiny dirt particles gives the water less to cling to, lessening the condensation.
  • Don’t leave wet items in the car - coats, umbrellas, dog towels etc just add to the moisture problem and mean mist will be more likely to form and take longer to clear.
  • Check for leaks - Even a small leak allowing damp to find its way into your car is enough to cause problems. Check areas such as window and door seals to make sure no water is creeping in, and check carpets and upholstery aren’t damp.
  • Use a dehumidifier - old cars in particular can be vulnerable to moisture creeping in, even if you’re not in the car. A portable dehumidifier pad will absorb some of this and help reduce condensation, and only costs a few pounds.
  • Try shaving foam - Bizarre as it sounds, wiping the inside of the windscreen with a little bit of shaving foam can help. Put a blob on a cloth, wipe it all over the screen then wipe it down with a clean cloth so the glass is clear. The detergent in the foam stops the water from beading and forming the dreaded mist.

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