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. Because of their high strength, carbon nanotubes may one day be used for bulletproof armor and other uses needing hard, lightweight materials. Some carbon nanotubes also let electricity through them. Certain nanotubes may be up to 1,000 times as good conductors as metals like copper and silver.