Carbon nanotubes are long chains of carbon held together by the strongest bond in all chemistry, the sacred sp2 bond, even stronger than the sp3 bonds that hold together diamond. Carbon nanotubes have numerous remarkable physical properties, including ballistic electron transport (making them ideal for electronics) and so much tensile strength that they are the only substance that could be used to build a space elevator. The specific strength of carbon nanotubes is 48,000 kN·m/kg, the best of known materials, compared to high-carbon steel’s 154 kN·/kg. That’s 300 times stronger than steel. You could build towers hundreds of kilometers high with it.