Skip to the content

Video: The science of windscreen defogging goes viral

IT TOOK a former NASA employee and mechanical engineer, Mark Rober, to ‘demistify’ the science behind windscreen defogging for American motorists – and many others across the world – recently with his posting of a YouTube video that immediately went viral.

The short clip had more than 2,600,000 million views when we caught up with it about a week after it was posted early in the New Year.

Its appeal comes from Rober’s clear and easy-going presentation that tackles common misconceptions about defogging and questions drivers often ask themselves when facing a foggy windscreen upon entering the car.

Should I blast it with hot air at full fan speed? Or would cold air work better? Should I use air from outside or hit the recirculation button? And will turning on the air-con, or opening the windows a bit, speed things up?

As you would expect from a former NASA man, Rober used his car to set up a consistent lab environment in which he could test the various combos, compare the results and, most importantly, come up with a definitive answer on the best way to defog the windsceen in less than half the time he says it would normally take.

After demonstrating what condensation was all about – and asking us to simply visualise air as a towel that can soak up water – Rober presented his four key steps to fast defogging.

Firstly, turn the heater on full blast, he says, because hot air can hold more moisture “so you’re increasing the size of your towel”. Secondly, turn the AC on, which pulls moisture out of the air as it passes over the cold coils of the air-con system, “so it’s like we’re wringing out our towel”.

Thirdly, make sure the recirc button is off. “Winter air is cold and we know it doesn’t hold much moisture, so if you bring it into your car and then heat it up, it has a lot of absorption capacity,” Rober says, before delivering his final step: opening all the windows slightly, even for a few seconds. “(This) helps by initially exchanging the humid air in your car with the dry air from outside.”

Rober also provided some tips to help reduce condensation forming in the first place, such as putting a sock filled with kitty litter on the dashboard. Rubbing an anti-fog liquid onto the glass can also help, although shaving cream, he says, works just as well.

Share on: FacebookTwitter