U.S. scientists say they've created a roof coating made from waste cooking oil that can switch roles season to season, either reflecting or using solar heat.

Roofs coated with the material would reflect summer sunlight and reduce air-conditioning bills. When chilly weather sets in, the scientists said their coating will transmit heat to help warm a building's interior.

"This is one of the most innovative and practical roofing coating materials developed to date," said Ben Wen, leader of the research project and vice president of the company that created the coating -- United Environment & Energy LLC of Horseheads, N.Y.

"This bio-based intelligent roof coating, compared with a traditional cool roof, could reduce both heating and cooling costs as it responds to the external environment," Wen said. "In addition, it will provide a new use for millions of gallons of waste oil after it is used to cook french fries and chicken nuggets."

By changing the coating's composition, Wen and colleagues said they can tune the substance so that it changes from reflective to transmitting at a specific environmental temperature.

The scientists said the coating might be commercially available in about three years.

The research, funded by the U.S. Department of Energy, was presented this week in San Francisco during the National Meeting of the American Chemical Society.