Carbon fiber can refer to carbon filament thread, or to felt or woven cloth made from those carbon filaments. By extension, it is also used informally to mean any composite material made with carbon filament. It is sometimes referred to as graphite-reinforced plastic. Its light weight and high tensile strength make it an ideal material for use in all types of R/C models.
Each carbon filament is made out of long, thin sheets of carbon similar to graphite. A common method of making carbon filaments is the oxidation and thermal pyrolysis of polyacrylonitrile (PAN), a polymer used in the creation of many synthetic materials. Like all polymers, polyacrylonitrile molecules are long chains, which are aligned in the process of drawing fibres. When heated in the correct fashion, these chains bond side-to-side, forming narrow graphene sheets which eventually merge to form a single, jelly roll-shaped filament. The result is usually 93-95% carbon. Lower-quality fiber can be manufactured using pitch or rayon as the precursor instead of PAN. The carbon can become further enhanced, as high modulus, or high strength carbon, by heat treatment processes. Carbon heated in the range of 1500-2000°C (carborizing) exhibits the highest tensile strength (820,000 Psi or 5,650 N/mm²), while carbon fiber heated from 2500-3000°C (graphitizing) exhibits a higher modulus of elasticity (77,000,000 Psi or 531 kN/mm²).
These filaments are stranded into a thread. Carbon fiber thread is rated by the number of filaments per thread, in thousands. For example, 3K (3,000 filament) carbon fiber is 3 times as strong as 1K carbon fiber, but is also 3 times as heavy. This thread can then be used to weave a carbon fiber cloth. The appearance of this cloth generally depends on the size of thread and the weave chosen. Carbon fiber is naturally a glossy black but colored carbon fiber has recently become available.
Carbon fiber is most notably used to reinforce composite materials, particularly the class of materials known as graphite-reinforced plastic. This class of materials is used in high-performance vehicles, sporting equipment and other demanding mechanical applications article.
Non-polymer materials can also be used as the matrix for carbon fibres. Due to the formation of metal carbides (i.e., water-soluble AlC) and corrosion considerations, carbon has seen limited success in metal matrix composite applications. Reinforced carbon-carbon (RCC) consists of carbon fibre-reinforced graphite, and is used structurally in high-temperature applications, such as the nose cone and leading edges of the space shuttle.
The fibre also finds use in filtration of high-temperature gases, as an electrode with high surface area and impeccable corrosion resistance, and as an anti-static component in high-performance clothing.
Some string instruments, such as violins and cellos, use carbon fiber bows. This is an alternative to the more common wooden bows.
High end frames for road bikes and mountain bikes are made of carbon fiber. Also, many road bikes made of aluminum have carbon fiber seat posts, handlebars and forks for reduced weight.
Carbon nanotubes are currently being investigated as possible improvements on the traditional carbon fiber material. While the nanotechnology field isn't advanced enough to create long-enough fibers made entirely of carbon nanotubes, research has shown that even as little as 5% (by weight) carbon nanotube constituents within the carbon fibers will dramatically improve properties. Andrews et. al. reported  that tensile strength increased by 90%, modulus increased by 150%, and electrical conductivity increased by 340%. This was in a pitch composite fiber with 5% (by weight) loading of purified single walled nanotubes (as compared to the corresponding values in unmodified isotropic pitch fibers). Further research is still needed to resolve issues such as nanotube dispersion and alignment, as well as interfacial bonding; however, this approach holds great promise for improving both the mechanical and electrical properties of carbon fiber composites.