Two types of nanotube exist: the single-walled carbon nanotubes, so called 'buckytubes', and multilayer carbon nanotubes. Both consist of graphite carbon and typically have an internal diameter of 5nm and an external diameter of 10nm. Many applications are envisaged: space and aircraft manufacture, automobiles, and construction. Multilayer carbon nanotubes are in commercial use. Buckytubes are some way off commercial production.