This story has been updated. It was originally published on June 8, 2018.
It’s a balmy 75 degrees outside, but as soon as you open the door of your parked car, an oppressive cloud of heat envelops you. Here’s how to keep your vehicle from getting so hot—even when you can’t find a shady parking spot—and how to cool it off as quickly as possible before you hop in.
Why your car is so stinking hot
On a sunny day, your car will always be hotter than the outside temperature, thanks to the greenhouse effect: The sunlight’s visible, short wavelengths can easily pass through glass windows, but once your car’s surfaces—think dashboard, seats, and carpet—absorb that light, the story changes.
Those materials store the energy and radiate it back out in long, infrared wavelengths, which cannot easily pass through glass. That means they can’t exit the car. Coupled with the still, unmoving air inside the vehicle, you have a recipe for serious heat. In fact, according to the National Weather Service, “a dark dashboard or seat can easily reach 180 to over 200 degrees Fahrenheit.” Yikes.
Crack the windows
In order to free that trapped heat, open your windows a crack when you park your car, creating an escape route for hot air. Believe it or not, one researcher actually tested this back in the 1980s: A study in Pediatrics found that cracking the window 5 centimeters lowered the temperature in a car by about 28 degrees on a 98-degree day. The interior air was still hot—it reached a stifling 122 degrees—but that’s still better than the 150 degrees they measured with the windows fully closed. Another study found a smaller drop in temperature on a cooler day, so the actual change in temperature will vary depending on the outside weather.
Opening the windows halfway kept the vehicle much cooler than opening them a crack, but this also makes it a little too easy for thieves to break into your car. So it’s best to settle for a smaller opening unless your car is parked in a very safe location.
Reflect sunlight from your windshield
Open windows aren’t the only way to prevent that light-to-heat conversion. You can also reflect some of the light back out your windows before the car’s interior absorbs it. That’s what sun shades aim to do, and they succeed fairly well: A series of experiments at the Florida Solar Energy Center (FSEC), a research institute run by the University of Central Florida, found that these shades can reduce the interior temperature of a car by 15 to 20 degrees. Researchers obtained the best results with shades that contained a reflective surface turned to face the interior of the car (yes, the interior).
That’s only a mild improvement in air temperature, but their real advantage lies in their ability to shade your dashboard: The FSEC found that sun shades cooled the steering wheel and other surfaces by a whopping 40 to 50 degrees, allowing drivers to touch them without burning their hands.
You can buy sun shades for $20 or less on Amazon, though some people swear by custom products like these Covercraft ones, which cost $65. The latter option is pricey, but covers the full windshield more easily and effectively than the cheap shades do.
Still, the windshield is just one of the entry points for sunlight. If you can get shades for your windows too, all the better, although removing shades from all your windows can be a bit of a hassle.
As a more convenient alternative, if you’re willing to spend more, a good ceramic window tint will also cut down on incoming light. It may run you a few hundred bucks, but if you live in a perpetually sunny area, the investment may be worth it.
Cover your seat and dashboard
If you find sun shades too expensive or annoying to wrangle, you can at least keep your seat, dashboard, and steering wheel from getting searing by keeping a beach towel or other cover in your car. Just drape it on the seat or dashboard when you exit to shield them from the sun. The air in the car will still get hot, but you’ll at least be able to sit down without burning your hands and legs.
If you want something a bit more elegant, cloth seat covers can protect your bare legs from sizzling leather seats.
Even if you forget a cover, you can try this trick to protect your steering wheel: When you park, turn the wheel so its top faces away from the direct sunlight coming through the windows. That way, you’ll have a relatively cool spot to grab when you return to the vehicle.
Cool your car quickly with this weird door trick
Unfortunately, while the above tips can help somewhat, your car will always wind up hotter than the outside temperature (unless you manage to leave the windows wide open). But you have one last resort for avoiding that sweltering heat: Force some of that hot air out before you get in.
To do this, open the driver-side door, roll down the passenger window, and then “fan” the driver’s door by opening and closing it several times in a row. This will recirculate the air quickly, making the interior comfortable enough for you to get in and start the air conditioner. Aaron Miller, cars editor at Thrillist, found this cooling method worked even faster than driving with the windows down. Sure, you’ll look a little silly in the parking lot, but it’s a small sacrifice compared to melting in the driver’s seat.