AbstractRigid poly(vinyl chloride) was reinforced with 10 to 40 phr of 1/4‐inch glass fiber. This improved flexural modulus up to 140 percent, flexural strength 40 percent, and heat‐deflection temperature 8°C; and reduced creep by 90–95 percent, and the coefficient of thermal expansion by 50 percent. Thus a typical Type I rigid vinyl with glass reinforcement had flexural modulus 1,164,000 psi, flexural strength 16,500 psi, notched Izod impact strength 5.1 fpi; creep only 12 percent of normal unreinforced material, coefficient of thermal expansion only 50 percent of normal unreinforced material, and heat‐deflection temperature 79°C. Such balance of properties elevates rigid vinyl from a commodity plastic up to an engineering thermoplastic, capable of much wider and more economical utilization in high‐performance a