It’s winter, which means that you’re going to have to deal with foggy windows when you start up your car. While lots of people have their own tips and tricks for the fastest ways to defog their car windows, YouTuber Mark Rober this week posted a terrific video that shows how you can use science to find the optimal way to make sure your car’s windshield gets defogged as quickly as possible.

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In short, you’re going to use a mix of hot air from your car’s heating system mixed with dry colder air from outside the car. So here are the four basic steps that Rober recommends taking:

  • Turn up your heater all the way to act as the primary moisture absorbent.
  • At the same time, flip on your car’s air conditioning to make the air inside the car drier.
  • Turn your inside air circulation off — you’ll actually want to have cold outside air coming into your car while you’re running the heat.
  • Crack your side windows a little bit to bring in even more cold, dry outside air.

The ideal, then, is to apply hot air directly to your windshield while doing everything else you can to make the air circulating through the car drier. Rober also recommends filling up a sock with some cat litter and placing it on your car dashboard right up against the windshield to suck up even more moisture.

Check out Rober’s full video for yourself below.

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