Sumio Iijima of NEC Laboratories in Japan discovered carbon nanotubes in 1991. Carbon nanotubes (CNT) are a particular form of fullerene. They are similar in structure to carbon-60 but are elongated to form tubular structures, 1–2 nm in diameter. They can be produced with very large aspect ratios and can be .1 mm in length. Typically, carbon nanotube deposits contain both SWNTs and MWNTs. In their simplest form, nanotubes comprise a single layer of carbon atoms arranged in a cylinder, known as singlewall carbon nanotubes (SWCNTs). They can also be formed as multiple concentric tubes (multi-wall carbon nanotubes) with diameters up to 20 nm and length .1 mm. A team led by Richard E. Smalley at Rice University has developed a high-pressure process (HiPco) that produces only SWNTs in multigram batches. CNTs have great tensile strength and are considered to be 100 times stronger than steel, while being only one-sixth of its weight, making them potentially the strongest, smallest fibre known.