Michael Sykes, a builder from North Carolina, has created a home that can heat and cool itself using only solar energy. The principle at work is "phase change." Sykes has engineered the resin in the wood he builds with to change phase at 70 degrees F. The resin goes from liquid to solid and back to liquid again at room temperature. The phase change allows the walls to soak up and trap vast amounts of heat during the day--cooling the room. At night, the wood releases the heat and warms the home. In this video, Ira talks with Sykes about how it works. Sykes won first prize for his Enertia Building System at the 2007 Modern Marvels Invent Now Challenge, sponsored by The History Channel and the National Inventors Hall of Fame Foundation.