Today, numerous types of high-performance fibers are commercially available. These fibers range from polymeric fibers, such as aramid and extended-chain polyethylene, to carbon fiber, boron fiber, and ceramic fibers such as silicon carbide, and alumina. As Figure 1.4 shows, when a load is applied parallel to the fiber axis, all of these fibers are much stronger and more rigid (per given mass of a material) than traditional metals such as steel or aluminum. However, each of these high-performance fibers has certain additional advantages. For example, in oxygen-free environments, carbon fibers can retain their strength at extremely high temperatures. Polymeric fibers are much lighter than carbon and ceramic fibers and transparent to radar. Ceramic fibers, on the other hand, are resistant to oxidation but lose strength at high temperatures. The advantages and deficiencies of these and other high-performance fibers are detailed in later sections of this report.

Figure 1.4. Specific strength and modulus of high-performance fibers and other materials "specific property" means the property divided by the density.

In a composite material the fibers are surrounded by a thin layer of matrix material that holds the fibers permanently in the desired orientation