A carbon nanotube is an allotrope of carbon that is shaped like a tube of carbon atoms. Carbon nanotubes are very tough and hard to break, but still relatively light. Some are very long. Because of their high strength, carbon nanotubes may one day be used for bulletproof armour and other uses needing hard, lightweight materials. A few carbon nanotubes also let electricity through them. Some may be up to 1,000 times better at conducting electricity than metals like copper and silver. 