You're on the motorway, it's bucketing down with rain, and your car windscreen is starting to steam up.
You mess about with the buttons and get it back to normal. Only thing is, you're not sure what it was that you pressed . . .
More to the point, you want to know how to stop your car windscreen from steaming up in the first place.
Because not only does having your vision impaired make it hard to see, it also means you'll be driving illegally.
Why Do Windscreens Mist Up?
The force of nature responsible here is actually . . . you.
Yep. Whilst wet weather usually makes it easier for your windscreen to mist up, it's actually your breath (and that of any of your passengers) which is largely to blame. It heats the air inside the cabin, leading to the formation of a 'mist'.
Any moisture turns to condensation when it hits air beside the windows that's below a certain temperature (often called the 'dew point').
And if you didn't understand all of that, then don't worry.
You just want to know how to clear the mist, right?
How to Demist Your Windscreen in Double-quick Time
Your first port of call should be the front and rear demister buttons, which are designed specifically to, you guessed it . . . demist.
The demister buttons will have a symbol of a curved rectangle with 3 squiggly lines running through it, so they're pretty easy to recognise.
But what if your car doesn't have them?
Well, not to worry. You'll just have to do things a little more manually.
Here's how . . .
Step 1: Stop (if safe and legal to do so)
Because messing about with the controls usually means taking your eyes off the road, so it's best to pull up in a safe, convenient place and give it your full attention.
Step 2: Turn On the Car Heaters
Turning the heater on helps warm the windows so that they are above the 'dew point', which isn't where you want your car to be on the temperature scale.
But don't begin straight away with boiling hot air. It's best to start off with lukewarm air and then gradually ramp it up to warmer air. Put it on full fan but not full heat, and point the vents towards your windscreen. (In a lot of vehicles, there's an option to automatically point all the heaters at your windscreen.)
If you have time, you can also use a cloth or pad to clean the inside of the windscreen. Obviously, best not drive whilst doing that.
Step 3: Turn On the Air Conditioning
Without turning the heaters off . . . because ideally you want both on at the same time in order for this method to work.
Using the air conditioning to demist your windscreen might seem counter-intuitive . . . its main purpose is to cool your car down, right?
Well, yes, but air conditioning can also be good way to demist your windscreen. It'll make sure that the air being directed towards the windscreen is dry, therefore preventing further moisture appearing on the glass.
Don't have air-con? Then go old school and roll down the car windows . . .
How Can I Stop My Car Windows Fogging Up?
Of course, the best way to tackle a problem is to stop it from happening in the first place. Attack is the best form of defence.
However, the truth is that there's no million-dollar answer here.
That being said, keeping your windscreen clean is going to go a long way towards stopping any mist from forming, whereas leaving it dirty tends to promote the build-up of condensation.
Sooooo . . . gather your arsenal of cleaning equipment and get to work. You'll need:
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Microfibre cloths
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Windscreen cleaning spray (or plain old water will do the trick, as well)
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Rubbing alcohol* (optional)
Then . . .
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Give the windscreen a once-over with one of the microfibre cloths, which will remove any debris that might be clinging to the inside of the glass.
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(Optional) Soak some of the alcohol into a folded cloth, then use circular motions to wipe down the windscreen.
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Using your liquid cleaner of choice, spray into a cloth and apply to windscreen. (Don't spray it directly on the windscreen, though.)
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Dry using one of your microfibre cloths.
Dehumidifiers will also do the job. They're designed to attract moisture, thereby removing it from the surrounding air and hence from your windscreen as well. Also, some companies sell anti-fog solutions which you can apply to the inside of your windows.
What About Shaving Foam?
This may or may not be a myth.
A lot of people will tell you to rub it onto your windows, and it's supposed to work just as good as the above method when it comes to stopping in the formation of mist.
Still, we'd advise staying clear of 'DIY' solutions like shaving foam, but as we haven't tested it, we can't give you a definitive answer one way or the other.
But as long as you don't mind the smell, then you're welcome to try.
Summary
Yes, windscreen misting can be a problem that springs up quickly. But luckily for you, it's also a problem that has a quick solution.
Remember: if you're already parked, don't move off until any glass surfaces and side windows are clear. Or if you're on the move already, stop in a safe place if possible.
FAQs
Do you use hot or cold air to demist a windscreen?
It's usually best to start off your heater on cold and then gradually increase the temperature bit by bit. Both hot or cold air will work, but hot air is usually seen as the more effective when it comes to demisting the windscreen quickly.
What is the quickest way to demist windscreen?
The best way to demist your windscreen quickly is using the demisters or, failing that, a combination of both your heaters and your air conditioning systems.