Nanocomposites are materials with a nanoscale structure that improve the macroscopic properties of products. Typically, nanocomposites are clay, polymer or carbon, or a combination of these materials with nanoparticle building blocks. Nanocomposites, which are materials with nanoscale separation of phases can generally be divided into two types: multilayer structures and inorganic/organic composites. Nanocomposites can greatly enhance the properties of materials. For example, ppm level impurities can result in the formation of nanoscale aluminide secondary phases in aluminum alloys, increasing their strength and corrosion resistance. Magnetic multilayered materials are one of the most important aspects of nanocomposites as they have led to significant advances in storage media. Nanocomposite coated tennis balls keep bouncing twice as long as an old-style ball because it is made of a mix of butyl rubber, intermingled with nanoclay particles, giving the ball substantially longer shelf life.