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The Fastest Way to De-Fog Your Windshield

Road & Track logo Road & Track 1/5/2018 Bob Sorokanich

Winter's here, and for lots of us, that means dealing with a foggy windshield full of condensation when we go to start our cars. In the grand scheme of things, it doesn't take that long for your defroster to clear your windshield, but if you're harried and already late for work, that extra time waiting can feel like an eternity. And we don't want you driving around through a half-obscured windshield like a dingus.

This post was originally published in January 2016. It's winter again, so we figured you could use this knowledge in 2018.

Former NASA Engineer Explains the Fastest Way to De-Fog Your Windshield© Mark Rober Former NASA Engineer Explains the Fastest Way to De-Fog Your Windshield

Luckily, former NASA engineer and current YouTube science guy Mark Rober has figured out a handful of easy tricks that will help you blast fog off the inside of your windshield in half the time. These aren't old wives' tales - this is science.

In this six-minute video, Rober explains exactly what causes water vapor to condense on the inside of your windshield, using stone-simple visual teaching aides and an explanation that a school kid could understand. Then, using a series of rigorous scientific experiments that would satisfy the evidence lust of any mechanical engineer, he tests all the different air conditioning settings you've probably got in your car to find the absolute quickest setting for blasting away fog.

Now, we should note: what Rober is doing is defogging the inside of the windshield. Defrosting, or removing frozen ice from the outside of the windshield, is a different matter altogether - one that you should use an ice scraper (and never, ever hot water) to resolve.

Anyway, here's the heater setting that Rober discovered clears fog the fastest:

  • Defroster fan on highest setting
  • Temperature control on its hottest
  • A/C turned on
  • Recirculate turned off
  • Crack your windows

For the science behind why this setting works best, and how fog forms in the first place, check out Rober's video above.

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