Aramid fiber is an organic fiber produced by axially aligned aromatic polyamide polymer molecules that are hydrogen bonded together into radial plates. Aramid is often combined with a polyester or epoxy matrix, offers exceptional tensile strength and toughness, but poor compressive and moisture resistant properties. The most widely used aramid fibers are Kevlar® and Twaron®.

Carbon fiber (sometimes called graphite fiber) possesses both high fiber modulus (>33 to 120+ Msi), and high fiber strength (>200 to 1000+ Ksi). Carbon fiber can be made from a variety of organic or petroleum polymer fibers. Most commonly, it is made from either of two precursor materials: pitch or polyacrylonitrile (PAN). Most standard intermediate modulus fiber is made from PAN, while pitch is used for the production of high modulus fibers. The precursor material is spun into fibers and processed in three steps: oxidation, carbonization, and graphitization. This processing forms a turbostratic graphitic structure in which graphitic crystallites are aligned with the fiber axis and intermingled with each other. The processing of carbon fibers produces three types of fiber:

• •High Modulus fibers have marginal strength and marginal elongation to failure.

• •Intermediate Modulus/Intermediate Strength fibers have higher elongation to failure.

• •High Strength fibers have standard modulus and elongation to failure.

Fiberglass is the most common material used for commercial fiber reinforced polymer composites. Called glass or fiberglass, this material is processed in several different ways to form products with varying features:

• •E-Glass is the most inexpensive and commonly used fiber. The "E" designation stands for "electrical" because of its superior insulative properties. E-Glass has good fiber strength (~500 Ksi) and relatively low fiber modulus (~10.5 Msi).

• •S-Glass is a standard aerospace formulation of glass that is stronger (~600 Ksi) and higher modulus (~12.5 Msi) than E-glass. The "S" designation is for "strength," and is a trade name of Owens-Corning Inc. Other fiberglass manufacturers with comparable products use designation such as "T-glass" and "R-glass."

• •C-Glass is a corrosion resistant type of glass, and is usually used as a surfacing veil cloth on outer surfaces of laminates, or against tool surfaces to protect the laminate from corrosion.
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