Skip to Content
MIT News magazine

Having It Both Ways

Color-shifting roofs could save energy
December 21, 2009

White cars are popular in sunny climates for good reason: they stay much cooler than darker ones, because white surfaces reflect sunlight instead of absorbing its heat. Likewise, U.S. Energy Secretary Steven Chu advocates using white materials for all roofing, to reduce the need for air-conditioning.

WHITE HOT A prototype tile designed to turn dark in cold weather and white in warm weather is white after getting a blast from a heat gun.

Critics counter that in cooler climes, black roofs are actually more energy efficient, because they capture more solar heat in cold weather. Now a group of students and recent MIT graduates has achieved the best of both worlds: a new kind of roofing tiles that would automatically turn black in cold weather and white in hot weather.

Lab measurements show that in their white state, the tiles reflect about 80 percent of the sunlight falling on them. That means they could save more than 20 percent of present cooling costs, according to recent studies. When they turn black, the tiles reflect only about 30 percent of sunlight, but the heating costs they would save over all-white roofs have yet to be quantified.

The team, called Thermeleon (rhymes with “chameleon”), won the $5,000 first prize in MIT’s annual Making and Designing Materials Engineering Contest in October. Team member Nick Orf, PhD ‘09, says the secret is a commercial polymer in a water solution. The solution is encapsulated between layers of glass and plastic, or between flexible plastic layers; the bottom layer is black.

Below a certain temperature (controllable during manufacturing by varying the composition of the solution), the polymer stays dissolved, and the backing shows through. But when the temperature climbs, the polymer condenses to form droplets small enough to scatter light, making a white surface. The researchers are also working on a microencapsulated solution that could be inexpensively brushed or sprayed onto any surface.

But can such roofing endure harsh winters and hailstorms? Time–and testing–will tell. “It’s got to stand up to very harsh conditions,” Orf says.

Keep Reading

Most Popular

This new data poisoning tool lets artists fight back against generative AI

The tool, called Nightshade, messes up training data in ways that could cause serious damage to image-generating AI models. 

Rogue superintelligence and merging with machines: Inside the mind of OpenAI’s chief scientist

An exclusive conversation with Ilya Sutskever on his fears for the future of AI and why they’ve made him change the focus of his life’s work.

The Biggest Questions: What is death?

New neuroscience is challenging our understanding of the dying process—bringing opportunities for the living.

Data analytics reveal real business value

Sophisticated analytics tools mine insights from data, optimizing operational processes across the enterprise.

Stay connected

Illustration by Rose Wong

Get the latest updates from
MIT Technology Review

Discover special offers, top stories, upcoming events, and more.

Thank you for submitting your email!

Explore more newsletters

It looks like something went wrong.

We’re having trouble saving your preferences. Try refreshing this page and updating them one more time. If you continue to get this message, reach out to us at customer-service@technologyreview.com with a list of newsletters you’d like to receive.