This document discusses fiberglass, which is glass that has been spun into fibers. It is commonly used as reinforcement in polymer matrix composites. There are different types of fiberglass including E-glass and S-glass, which have good chemical resistance, mechanical properties, and insulating properties. Fiberglass is desirable due to its low cost, high strength and stiffness, chemical resistance, and ability to maintain properties over a wide range of conditions. It is commonly used in applications such as transportation, electronics, construction, aerospace, and medical products.