Do Sunshades Really Cool Down a Parked Car?

It feels obvious, right? Throw a piece of cardboard or a reflective panel in front of your windshield and the car’s interior should stay cooler—just like curtains keep a room from heating up. Ancient Romans knew the trick, using wooden shutters to keep their palaces from turning into saunas. But does the same idea work for today’s rides?

Back in 1988, researchers at the University of Central Florida’s Solar Energy Center parked two identical Toyota Tercels on the hot Cape Canaveral lot. They taped a simple cardboard sunshade behind the windshield of one car and a foil‑backed shade on the other, then measured cabin and dashboard temperatures. The results were eye‑opening: a car left in the sun can push interior temps up to 150 °F, while the dashboard can scorch close to 200 °F. Slip a cardboard shade in behind the glass and the cabin drops about 15 °F, with the dashboard shedding a whopping 40 °F. Adding a foil reflector shaves off another 3‑5 °F inside and 6‑11 °F on the dashboard. In short, interior shades help, but they’re not the ultimate solution.

Researchers in Malaysia took the idea a step further. A 2012 paper presented at the International Conference on Mechanical, Automobile and Robotics Engineering in Penang tested a cheap nylon shade over the front windshield. The shade knocked a blistering 189.5 °F dashboard temperature down by more than 30 °F. That’s impressive for a piece of fabric you can buy for a few dollars.

Europe’s biggest motorists’ club, Germany’s ADAD (Allgemeiner Deutscher Automobil-Club), ran a 2026 study comparing a handful of passive‑cooling tricks. The clear winner? A partial exterior car cover. Covering the roof and front fenders lowered the cabin from a sweltering 127 °F to just under 110 °F. An external reflective shield over the windshield performed almost as well, cutting the interior to about 113 °F. By contrast, slipping the same shield inside the glass barely helped, with cabin temps still hovering around 120 °F. Even a plain white cloth inside the car only nudged the temperature a couple of degrees higher.

So why bother with shades at all? The Department of Energy warns that blasting the A/C at full tilt can slash fuel economy by up to a quarter. A quick external shade can keep the cabin cool enough that you won’t need to crank the compressor, saving gas and keeping the engine from working overtime.

Color matters, too. ADAD found that a black car under midday sun reached a surface temperature of 149 °F, while a white one stayed near 111 °F. Inside, the black car hit 127 °F versus 118 °F for the white. Lawrence Berkeley National Lab’s 2011 research echoed this, showing that cooling a silver car to a comfy 77 °F used about 13 % less A/C energy than a black counterpart. Dark vehicles also contribute to higher urban heat islands, so a lighter shade isn’t just good for you—it’s good for the neighborhood.

And, a reminder that goes beyond comfort: never leave a child unattended in a parked car. Consumer Reports found that even on a mild 61 °F day, the interior can climb to 105 °F in just an hour—enough to cause deadly heatstroke. An exterior sunshade can buy precious minutes, but the safest move is to keep kids out of the car entirely when it’s parked.

Bottom line: interior cardboard or nylon shades do lower temperatures, but an outside cover or reflective windshield shield does the job better. Pair that with a light‑colored car, park in the shade when you can, and you’ll keep the cabin from turning into an oven without draining the fuel tank.