U.S. Secretary of Energy Steven Chu made waves last May when he suggested during a Nobel Laureate summit on climate change that painting all the world’s roofs white could reduce carbon emissions by as much as 24 billion tons. It’s a principle builders know well -- light colors reflect the sun’s energy, while dark roofing absorbs heat, forcing HVAC systems to work harder in hot months. But what about those stretches of harsh winter when the heat absorption is appreciated? Wouldn’t it be nice to have roofing that acts like a “mood ring,” staying dark in cold temperatures, but morphing to light when the thermometer goes up? 

A prototype technology conceived by a team of MIT graduate researchers does just that. “Thermeleon” roofing tiles, which recently received top prize in the university's third annual “Making and Designing Materials Engineering Contest,” consist of a common polymer and water solution sandwiched between layers of flexible plastic, with a dark layer of plastic used as backing. In cold temperatures, the polymer remains dissolved in water and the black backing shows through. In hotter conditions, the polymer condenses to form tiny droplets that scatter light and produce a white reflective surface. 

Early lab studies have pegged the tiles’ reflective properties at about 80% when they are in their white state, versus 30% when they are black. The research suggests that tiles that convert to white could offset as much as 20% of current home cooling costs during hot months.

And that’s not all. In the next iteration of product development, the Thermeleon team is investigating the possibility of micro-encapsulating the polymer solution in a clear paint material that could be brushed or sprayed onto existing surfaces. If brought to market, such a product could pose an eco-retrofitting solution for built homes that would prove far more cost-effective than installing all new roofing.

The big questions that remain relate to long-term durability. “It’s got to stand up to very harsh conditions,” Nick Orf, a member of the product development team noted in an article on MIT's website. “Those sorts of tests would have to be done before we’ll know if we have a viable product.”

Jenny Sullivan is a senior editor covering design for BUILDER.