The major component of composite materials is the fiber reinforcement. The fiber reinforcement provides strength and stiffness in the direction that the fibers are aligned. The three most common fiber types found in aerospace applications are carbon fiber, glass fiber, and aramid fiber. These fiber types have different chemical compositions at the molecular level which generate different physical and mechanical properties at the macroscopic fiber level. Important properties of fibers include their strength, modulus, toughness, temperature capability, density, conductivity, chemical compatibility, fatigue life, and cost.