The automobile industry is also attempting to develop production techniques to put plastics on mass-produced vehicles (notably GM's Saturn car lines), but even here the plastic components are not critical structural elements of the vehicle. All Saturns, for instance, use plastic body panels to cover a steel space frame. Because they have no structural role, the panels are made not of reinforced composites but of ordinary plastics, which can be produced in quantities of hundreds of thousands. The choice of material is governed less by weight considerations than by cosmetics: plastic panels give the vehicle its distinctive shape and resist dents and scratches. In fact, the weight saving achieved by the use of plastic panels is at least partly offset by the need to use more steel in structural components to maintain the expected level of performance.

Automakers have found that, with an aggressive effort, they can substitute polymers for steel in a handful of major nontraditional applications, such as roofs, hoods, floor pans, and engine cradles, but many are also discovering that the costs are too high and the weight savings unimpressive. GM has also experimented with glass fiber composites on the body panels of its APV vans for a number of years but recently concluded that the material is just too expensive. The company plans to return to using steel.

While they continue to experiment with glass fiber-reinforced polymers in niche-market vehicles--a well-established platform for innovation--automakers appear to have decided that these materials are not useful in applications with production volumes over 80,000, because at these volumes the benefits do not justify the costs. Moreover, it appears that the industry is already using plastics in most of the applications that are best suited to the material's strengths. Further substitutions of plastics for steel will be much harder to accomplish, because these are the uses that capitalize specifically on the properties of metals.