This summer, heat waves hit the Northern Hemisphere with temperatures upward of 100°F, highlighting one of the biggest current worldwide challenges: keeping buildings (and the people inside them) cool. A group of researchers from Columbia University may have an answer. They’ve designed a new material that chills buildings by reflecting sunlight.

Instead of getting rid of heat that has already slipped into the building, this new material keeps heat from entering in the first place. The material takes advantage of “passive daytime radiative cooling,” the idea of bouncing the sun’s radiation back out into the frigid expanses of outer space. In the past, people have attempted to paint buildings colors that reflect more light (like white), but these paints still contain light-absorbing pigments that trap the heat. The new material instead utilizes tiny holes—only a few nanometers or micrometers wide—to capture and reflect sunlight. The researchers tested it out on buildings in three cities with different air conditions: dry Phoenix, Arizona; particle-filled New York City; and hazy Chattergram, Bangladesh. The material was able to hold up in all three, cooling buildings by up to around 10°F under optimal conditions in Phoenix, but even achieving 5°F decreases in the moisture-filled air of Chattergram.

If this coating is adopted on a broader scale, it could dramatically decrease the current energy footprint of cooling processes. Air conditioning, for example, delivers a chill but requires constant electricity, which in turn contributes greenhouse gases to the atmosphere, creating a positive feedback loop. The new material is a versatile alternative that can just be sprayed or painted onto a surface and help stop the feedback loop. And, if you want a splash of color, don’t worry: Adding pigments only slightly decreases the coating’s effectiveness.

Managing Correspondent: Aparna Nathan

Original article: Hierarchically porous polymer coatings for highly efficient passive daytime radiative cooling – Science

Media coverage: This New Coating Could Help Keep Buildings Cool – Smithsonian Magazine

Cooling paint drops the temperature of any surface – Science

Related SITN Articles: Heat waves hurt your brain: the argument for window AC units

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