For several years, Wilson Sporting Goods lined its high-end Double Core tennis balls with a composite made from butyl rubber and vermiculite and developed by nanotech company InMat. The clay nanoparticles would spread out like sheets of paper scattered across a floor and keep air molecules from escaping, which kept the balls firm for an unusually long time. But American tennis players didn't want to pay more for a ball that lasted longer, so Wilson discontinued it.