With the development of pressurized fuel systems, the evolution of vehicle designs, and the increasing variety of fuels available, the environment an automotive fuel system encounters is becoming increasingly difficult. A fuel line made of Nylon 12 can meet all environmental and flexibility requirements of the fuel system. As a result, Nylon 12 is the most widely used, nonmetallic fuel line material.For a thermoplastic fuel line, dimensional increases (mostly length change) can vary widely from the swelling caused by the different fuels encountered. Nylon 12 is affected the least of all the nylon resins. The use of plasticizer further decreases the swelling that can occur with Nylon 12, but does not eliminate the dimensional changes completely. A method has been devised to produce Nylon 12 tubing that has no length change, even in fuels that are very aggressive chemically.