Most - if not all - drivers have at some point encountered condensation on the inside of their car windows. Clearing condensation can be time-consuming - but it’s essential so you can see other road users and do not fall foul of the law.

The Highway Code states you must have a clear view out of all your windows. This is backed up by Section 41D of the Road Traffic Act 1988, which stipulates that you must have a clear view of the road before you move off.

How does condensation develop?

Condensation forms when the temperature and moisture levels inside and outside of your car are different. Because your car's cabin is enclosed, dampness and heat can build up.

When warmer moisture particles come into contact with a cold windscreen, visible vapour converts to tiny droplets of water, which forms mist on the inside of the glass.

One of the main causes of condensation is people breathing, although naturally this only occurs when a journey is undertaken. However, condensation can also build up overnight or while the car is otherwise parked up.

What contributes to condensation?

Certain items you keep in your car may increase the level of dampness. These include dog blankets, umbrellas and coats. It's a good idea to remove items like these whenever you are not driving.


Leaks can develop in various parts of your car, including the heater matrix, the doors, or sunroof seal.

It can be challenging to pin point such a leak, but a trained mechanic should be able to help. In some cases the only way to locate a leak is to strip down a vehicle in its entirety, which might not be economically viable - especially for an older car.

As your car ages, the chances of a leak developing increases, especially after the six-to-seven year mark.

Combating condensation

Wash down your windows, both inside and out. As grime accumulates it gives moisture something to adhere to - so removing it could be beneficial.

Use a specialist automotive cleaner and polish, along with a cloth or newspaper.

Cleaning your car on a regular basis will help keep dirt and grime at a minimum and therefore reduce condensation.

Absorb moisture

Tackle condensation by placing moisture-absorbing items in your car. One effective measure is filling an old sock or pair of tights with cat litter. The clay particles in cat litter are excellent at absorbing excess moisture.

Air out your car

If the weather is relatively dry and it is safe to do so, leave your windows open to allow your car to air out.

Clear condensation before moving off

As mentioned, your are legally bound to clear your windows before you begin your journey. The most common way to do this is to turn on the heater or heated windscreens:

  • If your vehicle has heated windscreens, turn them on.

  • Turn on your blower full-blast but without heat to begin with and aim it at your windows. Gradually increase the heat over a few minutes.

  • If you have one installed, use your air-conditioning system to dry the air.