With a typical diameter of 7 μm, carbon fibers are about one-tenth the thickness of a human hair. They are produced from carbon-containing polymer fibers. These precursors are preferably based on polyacrylonitrile (PAN), but coal tar pitches and petroleum pitches (isotropic pitches and mesophase pitches) or cellulose are also used. The processes that are understood as carbon fiber production in the narrower sense are stabilization of the precursor fibers at 200 to 300°C in air, carbonization at 1300 to 1500°C under an inert gas (nitrogen), and, if necessary, a downstream furnace stage above 1800°C known as graphitization. Following these processes, the carbon fibers undergo electrochemical surface activation and are given a special finish to make them easier to handle in later textile processing steps.
Properties of commercial carbon fibers: Commercial carbon fibers today can be classified into two basic families:

• high-tensile carbon fibers HT
• high-modulus carbon fibers HM

The high-tensile carbon fibers based on polyacrylonitrile (HT) have typical strength values of 3500 to 5000 MPa and elastic modu­lus values between 230 and 270 GPa. The high-tensile carbon fiber family also includes a group with an intermediate elastic modulus (IM).These types have strength values up to about 7000 MPa with a typical elastic modulus be­tween 280 and 300 GPa.
The high-modulus carbon fibers can reach a typical elastic modulus of 550 GPa (HM) up to 900 GPa (UHM).
A feature common to all carbon fibers is their superior performance/weight ratio. With a typical density if about 1.8 g/cm³, they are 75% lighter than steel. Compared with the even lighter aramid fibers, they have at least twice the stiffness. This superiority over all current structural fibers makes modern carbon fibers an outstanding material for a wide variety of high-performance applications.