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It’s All in the Paint

A newly developed white paint can keep buildings cooler by reflecting nearly all of the Sun’s rays.

Light from a smiling Sun wearing sunglasses beats down on white rooftops and then bounces off.

© Marrishuanna, Natthaya Phiban/Dreamstime.com; Animation Encyclopædia Britannica, Inc.

Did you know that the temperature of a building is affected by the color of its roof? Lighter colors reflect much of the Sun’s heat, while darker colors absorb it. With that in mind, a scientist at Purdue University in Indiana has invented a new white paint that’s designed to keep a building cooler, just by coating its roof.

White roofs aren’t a new idea. In fact, they’re widely used in many cities that experience hot temperatures because they’re known to decrease the need for air-conditioning. But most white paint reflects about 80 to 90 percent of the Sun’s rays. The rest of those rays are absorbed into the building.

A few years ago, Xiulin Ruan, a professor at Purdue University, set out to make a more reflective white paint. “We wanted to help with climate change, and now it’s more of a crisis, and getting worse,” Ruan told the New York Times. “We wanted to see if it was possible to help save energy while cooling down the Earth.”

It’s a welcome development at a time when record-breaking heat waves in North America, Europe, and Asia have made headlines.

The paint that Ruan and a team of scientists developed reflects more than 98 percent of the Sun’s rays. At midday, a surface that’s been covered with the paint remains up to 8 degrees Fahrenheit (4.5 degrees Celsius) cooler than the air that surrounds it. At night, it’s up to 19°F (10°C) cooler. According to Ruan, the paint can decrease the need for air-conditioning by up to 40 percent.

The Purdue scientists achieved this level of reflectiveness by making the paint from a very reflective compound called barium sulfate. One downside is that barium sulfate must be mined, which is bad for the environment. But Ruan pointed out that most paint is made with titanium dioxide, which also has to be mined.

On the plus side, the new paint could help address some of the effects of climate change, provided it’s used widely enough, by reflecting those warming solar rays back into space. Ruan and his team have since developed a thinner form of the paint that can be used on airplanes, cars, and other vehicles to reduce the need for air-conditioning, even if they’re sitting on a hot tarmac or in a sizzling parking lot.

So, when can people go out and buy the ultra-reflective white paint? Ruan says he hopes it will be available as soon as 2024.

Did You Know?

© Christian Delbert, Artinspiring, Ramcreativ/Dreamstime.com; Animation Encyclopædia Britannica, Inc.

An air conditioner can cool a home to only about 15 to 20 degrees below the outside temperature.

Keeping Your Cool in the Summer

© New Africa/stock.adobe.com

Is your home sweltering in the summer? Before you crank up the air-conditioning (if you’re lucky enough to have air-conditioning, that is), check out these tips for beating the heat at home.

    • If you have a ceiling fan, use it! Ceiling fans don’t actually cool the air, but they can make a room feel cooler. Most ceiling fans have a switch at the base that allows you to change the direction they spin. (Turn the fan off before you change its direction.) It’s important to make sure the fan’s blades are moving counterclockwise in the summer, creating a downward breeze.
    • Close blinds and curtains. Sure, afternoon sunlight can make a room feel toasty in the winter. But that heat becomes a lot less welcome in July. In the summer, be sure to close your blinds or curtains before the Sun has a chance to heat things up. It also helps to put plants in front of windows that get a lot of sunlight.
    • If the evenings or early mornings are fairly cool, take advantage! Open the windows, if possible, but be sure to close them before the day heats up. You can also put a box fan in the window to help bring that cool air inside.
    • If it’s super hot, try putting a bowl of ice in front of a fan. This will create the effect of an air conditioner—until the ice melts!
    • Wear light-colored clothing. Like white paint, light-colored clothing will absorb less heat than dark clothing.
    • Turn down the air-conditioning. If you must use the air conditioner, try setting the thermostat (the part that determines the indoor temperature) one degree higher. This will save energy while still cooling you down.


    Remember, extreme heat can be dangerous, especially for the very young, older people, and pets. If the temperature is high, take it easy and drink plenty of water. And if you or family members need some relief, see if it’s possible to go to a store, a library, or another public place that’s air-conditioned.

How Sunlight Can Help

© deepblue4you—E+/Getty Images

Solar panels help capture the energy of the Sun.

Painting a building’s roof white deflects the Sun’s warming rays. But we can also harness the power of the Sun in a way that’s hugely helpful. Solar energy is less costly and less harmful to the planet than some other forms of energy, partly because the Sun’s energy is renewable, meaning it won’t run out.

You can learn more about solar energy at Britannica School.

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