When it came time to purchase my second car, I had only one requirement: a rear window defroster. My first car, a 1976 Plymouth Volare, didn't have that feature, and taking the time to scrape off my windshield in my college apartment complex often meant I'd be late to class. (It probably didn't help that I was usually doing it with a cassette case instead of an ice scraper.)

I often think about that car and the cassette cases when I walk out my front door to a frosty car. With modern defrosters, it takes much less time to defrost a windshield than it did way back when, but it still can set me and my kids behind a few minutes.

How to remove frost quickly

If you want to remove the frost from your windshield quickly, there's a brilliant way to do it using things you probably already have on hand.

Create a mixture of 2/3 isopropyl alcohol (also called rubbing alcohol) and 1/3 water and put it in an empty, clean spray bottle. Spray it on a frosted windshield, and the alcohol — which has a freezing point of minus 128 degrees Fahreinheit — will instantly clear up the problem. You can see it in action in the video below:

And because of the alcohol's very low freezing point, the mixture in the spray bottle can be left inside the car without freezing, so you'll never be without it when frost strikes.

What causes frost on a windshield anyway?

Freezing temperatures mean frosted windshields, right? Not necessarily.

This morning when I woke up, it was 21 degrees outside, yet my windshield was clear when I went to take the boys to school. A temperature below freezing is not the only factor when it comes to frosted windshields; the ground temperature, the amount of moisture in the air and the wind also matter.

It's the overnight temperature near the ground, not the temp higher in the air, that causes a frosted windshield, according to The Why Files. Yesterday, the temperature was about 45 degrees during the day. The ground temperature overnight probably never got below freezing. It was also a very windy night, and any moisture that might have created frost on my windshield didn't have the opportunity to become frost.

So, when the conditions are right — freezing temperatures near the ground, moisture in the air, and little wind — you will probably walk out your door to find a frosty windshield.

Good thing you've got that spray bottle of alcohol and water, right?

Robin Shreeves ( @rshreeves ) focuses on food from a family perspective from her home base in New Jersey.