Car windows fog up when warm, moist air comes into contact with the cold glass surface. The warm air condenses and causes the mist or fog on the windscreen and windows.
Wiping the window with a clean cloth or demisting pad is a quick fix, but won’t stop more condensation from forming, and can leave streaks so it’s better to use the ventilation system if you can.
How to demist your windows:
Make sure the air is directed at the windscreen and windows and turn the fan up full. Keep the temperature low to start with; overloading the car with hot, wet air will just add to the problem. The cold air from the fans will still be warmer than the glass and help dry it out and then you can start to turn up the heat.
If you’ve got air conditioning use it; it will help to dry the air out more quickly. Don’t use recirculation – this will warm the car quicker but just keeps the moisture trapped inside. Let cool fresh air in and the old, damp air out.
Open the windows, especially if you don’t have air conditioning or climate control – opening a window will help clear the screen faster as the cold, dry air from outside will help reduce the moisture inside and then you can start to raise the temperature.
How to stop it from happening:
Clean your windows – removing tiny dirt particles gives water less to cling on 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.
Use a dehumidifier – older cars in particular can be vulnerable to moisture creeping in, even when 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.
Check when you last replaced your cabin filter. This filter traps debris from the outside and prevents it from coming into the car. Most manufacturers advise replacing this every two years. It’s worth checking when this was last changed as a dirty clogged up filter can contribute to your windows steaming up.