On a cold morning in a parking lot, you may have spotted it: a plastic bag tied over each side mirror of a car. Online, the sight has inspired ads, rumors and a fact-check. The real answer is far more practical than most of the theories, and it’s especially useful this time of year.
In short
- Most of the time, it’s protection: a bag over the mirror keeps frost, ice and snow off the glass overnight.
- The Farmers’ Almanac puts it simply: bags on at night, frost-free mirrors in the morning.
- Some drivers also use it against birds, dust, or to hold a broken mirror together on the way to the shop.
- A white cloth on a car can also be a call for help, and a bag must always come off before you drive.
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What it usually means
Fact-checkers at Snopes looked into it and found a simple explanation: covering side mirrors helps in winter. They quote a 2016 Bob Vila tip: “The plastic covering will keep most of the ice and snow from sticking.” The Farmers’ Almanac gives the same advice: “Place plastic bags over your car mirrors at night and they’ll be frost-free in the morning.”
The payoff comes in the morning. As SlashGear notes, it lets drivers skip scraping the mirrors while the windshield defrosts.
The other reasons
SlashGear lists a few more. A bird fixated on its reflection can perch on the mirror, leave droppings and even scratch the paint, and a cover stops it. Near a construction site, a bag keeps dust off the glass. And some drivers wrap a cracked mirror so glass doesn’t fall on the road on the way to a repair shop, although the site adds that driving with a broken side mirror is illegal in many states. The idea that a bag deters mirror thieves doesn’t hold up, it says.
The rumor, and the real signal
Snopes traced ads running since at least December 2020 that promised “Put A Ziplock Bag Over Your Car Mirror, Here’s Why,” then never explained it. There is, however, a real signal close to it. North Carolina’s driver handbook, quoted by Minnesota’s New Country, says: “If you need help, tie a white cloth to the left door handle or the radio aerial.” A white bag on a car stopped on the roadside can mean a stranded driver.
The limit
Bags are for a parked car only. Driving with covered mirrors “is clearly a terrible idea that’ll impair your visibility,” SlashGear warns. It also suggests purpose-made covers with drawstrings, which leak less and go on and off faster than a grocery bag.
For the windshield, here’s what spraying vinegar on it is for. On the road this season, know the reflex to avoid if a deer runs in front of your car, and what the blue reflectors on the road mean.
One bag per mirror at night, off before you drive. That’s the trick.
