The fast rise of this durable exterior door material underscores its remarkable characteristics. Can anything top a quality fiberglass door? It’s a bold question to ask because of the material’s brief time in the marketplace. The first fiberglass exterior door was introduced less than 40 years ago. Wood and steel, the material’s leading competitors, have been around much longer. Why fiberglass? It starts with the material itself – a thermoplastic resin reinforced with glass fiber. Cheaper and more flexible than carbon fiber, fiberglass is stronger than many metals by weight, is non-conductive, and can be molded into almost any shape, including the skin of an exterior door.