Each carbon filament thread is a bundle of many thousand carbon filaments. A single such filament is a thin tube with a diameter of 5–8 micrometers and consists almost exclusively of carbon.
The atomic structure of carbon fiber is similar to that of graphite, consisting of sheets of carbon atoms arranged in a regular hexagonal pattern. The difference lies in the way these sheets interlock. Graphite is a crystalline material in which the sheets are stacked parallel to one another in regular fashion. The chemical bonds between the sheets are relatively weak, giving graphite its soft and brittle characteristics. Carbon Fiber is an amorphous material: the sheets of carbon atoms are haphazardly folded, or crumpled, together. This interlocks the sheets, preventing slippage and greatly increasing the strength of the material.