http://interestingengineering.com/new-aluminium-foam-promises-faster-stronger-and-lighter-trains/ The material consists of a 25 mm thick layer of the “foam,” actually a low-density, sponge-like composite of magnesium, silicon, and copper, and aluminum, which is sandwiched by two 2 mm thick aluminium sheets. There is no glue either, it’s all held together by metallic bonds. via New Aluminium Foam promises faster, stronger and lighter trains |Interesting Engineering.