The team's lab measurements show that in their white state, the tiles reflect about 80 percent of the sunlight falling on them, while when black they reflect only about 30 percent. That means in their white state, they could save as much as 20 percent of present cooling costs, according to recent studies. Savings from the black state in winter have yet to be quantified...

they use a common commercial polymer (in one version, one that is commonly used in hair gels) in a water solution. That solution is encapsulated — between layers of glass and plastic in their original prototype, and between flexible plastic layers in their latest version — with a dark layer at the back.

When the temperature is below a certain level (which they can choose by varying the exact formulation), the polymer stays dissolved, and the black backing shows through, absorbing the sun's heat. But when the temperature climbs, the polymer condenses to form tiny droplets, whose small sizes scatter light and thus produce a white surface, reflecting the sun's heat.

The team is still working on their product; their current research focuses on the idea that the polymer solution would be micro-encapsulated and the tiny capsules carried in a clear paint material that could be brushed or sprayed onto any existing surface.

The team won first place in the Making and Designing Materials Engineering Contest (MADMEC); the competition is intended to encourage the development of innovative materials that improve energy efficiency.

Frank Herbert had a very similar idea for his epic novel Dune. In the story, chromoplastic "tiles" are used to encourage evaporation for the purposes of plant irrigation.

"Each bush, each weed you see out there in the erg," she said, "how do you suppose it lives when we leave it? Each is planted most tenderly in its own little pit. The pits are filled with smooth ovals of chromoplastic. Light turns them white. You can see them glistening in the dawn if you look down from a high place. White reflects. But when Old Father Sun departs, the chromoplastic reverts to transparency in the dark. It cools with extreme rapidity. The surface condenses moisture out of the air. That moisture trickles down to keep our plants alive."