Living metal was a metal which was able to grow. It was discovered by Professor J. P. Kettlewell. He used it to create the Experimental Prototype Robot K1. (TV: Robot) The Time Lords utilised living metal. One type, if not the only one, was validium. (TV: Silver Nemesis) The outer plasmic shells of Battle TARDISes were living metal, able to morph into shields or any number of predetermined gun emplacements. (PROSE: Engines of War) The Architectural Reconfiguration System of the Doctor's TARDIS was built from a type of living metal. (TV: Journey to the Centre of the TARDIS)