Carbon nanotubes (CNTs) are tube structures composed of carbon atoms with nanometer-sized diameter and a micrometer-sized length. The length to diameter ratio of CNTs typically exceeds 1000. Within CNTs, the carbon atoms are arranged in hexagons (graphite shares this same arrangement). The structure of CNTs consists of an enrolled cylindrical graphitic sheet (graphene) rolled up into a seamless cylinder with a diameter of the order of a nanometer.

There are two main types of CNTs, single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). SWCNTs are a single layer of graphite, and since their length to diameter ratio exceeds 1000, they are considered a one-dimensional structure. SWCNTs are strong, conduct electricity, and are believed to conduct heat more efficiently than diamond. SWCNTs exhibit different electric properties than that of MWCNTs. SWCNTs are very expensive to produce, and therefore the development of a more affordable synthesis technique is integral to the future of CNT technology. MWCNTs are a collection of concentric SWCNTs, consisting of multiple layers of graphite rolled up to form a tube shape with varying diameters. The length and diameter differ between MWCNTs and SWCNTs, therefor their properties are very different. Compared to SWCNTs, MWCNTs possess increased mechanical stiffness, and MWCNTs are easier and more affordable to produce.

The gif depicts the rolling formation of SWCNT and MWCNT segment structures, created using AutoDesk Inventor Professional and converted to gif format using ffmpeg. The structures are depicted in a form of skeletal structure, with the representation of covalent single bonds as single lines, and all elements besides carbon and hydrogen are denoted with their symbol or functional group. In this example, both the SWCNT and MWCNT are composed entirely of carbon and hydrogen. Note that this figure is a segmented representation of CNTs, as the length to diameter ratio of CNTs typically exceeds 1000.