But researchers at Washington University in St. Louis have found a new use for bricks: as energy storage units. The bricks are powerful enough to illuminate an LED light bulb and cost only about $3 to make. The brick battery relies on the reddish pigment known as iron oxide, or rust, that gives red bricks their color. The scientists pumped the bricks with several gases that react with iron oxide to produce a network of plastic fibers. And right now the energy storage capacity of the bricks is still pretty low—about 1 percent of a lithium ion battery.