High-performance plastics are finding increased relevance as a way to make cars less costly to manufacture−and fill up at the gas pump

But weight reduction isn't the only quality that automakers look for in plastics. Plastics reduce costs when they replace traditional materials like steel, a benefit that automakers can't ignore, especially now when companies like Ford Motor Co. and General Motors are struggling financially. Plastics also allow greater flexibility for car makers to differentiate themselves through design.

Over the past three decades, plastics have made steady progress in automotive applications. According to an annual survey of automotive materials compiled by the trade publication American Metal Market, the content of plastics in automobiles has increased from 168 lb, or 4.6% of the average vehicle's weight, in 1977, to 249 lb, or 7.6% of vehicle weight, in 2000.

American Metal Market no longer conducts its survey. But according to the American Chemistry Council, the combined plastics and composites content of the average North American light vehicle has increased from 286 lb, or 7.3% of vehicle weight, in 2000, to 335 lb, 8.3% of vehicle weight, in 2004.

Much of the success of automotive plastics thus far has been due to their ability to reduce costs. This isn't necessarily because a pound of plastic costs less than the 2−3 lb of steel it replaces. Deborah F. Mielewski, a plastics research technical leader at Ford, explains that it is because a single injection-molded plastic part can do the job of many metal pieces welded together. "Plastics can be molded into far more complex shapes than you can stamp steel," she says. "And many times you can mold in attachments and brackets and consolidate pieces with plastics, reducing the number of parts in the assembly process."

Maria Ciliberti, automotive regional sales manager for Ticona, the engineering plastics unit of Celanese, says the utility of plastics in an automotive application largely depends on the complexity of the part. "If the part is just a piece of sheet metal, then it is really hard to compete with," she explains. "If you have multiple pieces of metal welded together, or if you have a lot of bending and shaping and other secondary steps to be done to the metal part, then this is really where plastic's forte lies."

The desired volumes of the part come into play as well, observers say. For example, when a production run of a vehicle is fewer than 50,000 to 100,000 units annually, an injection-molded plastic part is cheaper than one made from stamped steel. The expensive tooling required for steel is only justified if it can be used to crank out a larger number of parts.

Injection-molded plastics can also provide aesthetics that are difficult to obtain with traditional materials like steel and glass. A visible example is how automotive head lamps have changed over the past 20 years. Glass headlamp lenses began to be replaced with polycarbonate ones in the 1980s, according to Clemens Kaiser, chief executive officer of Exatec, a joint venture between Bayer and GE Plastics, which is developing technology to make automotive glazing out of polycarbonate.

Initially, the polycarbonate lenses were made similar to the square and circular glass they replaced. But gradually, automakers took advantage of the new material's versatility and made more complex and attractive shapes. "If you look at today's headlamp lenses and covers, you can see the advantages that polycarbonate provides," Kaiser says. "They are all shaped differently. They become part of the face of the vehicle and part of the design, and they are extremely important to the identity and brand of the vehicle."

Weight reduction was previously a favorable side effect of using plastics to reduce costs or give a car a sharp look. But because of concerns over high gas prices, weight is now becoming a more conscious consideration for car designers when they decide to go with plastics.

Americans are becoming aware of fuel efficiency in a way they haven't in years. SUVs are falling out of favor after ruling Detroit's automakers for nearly a decade. The automotive market consulting firm Autodata, for example, says U.S. sales of such light trucks slipped by 1.9% in the first four months of this year compared with 2005, while passenger car sales increased by 1.6%. Additionally, the Department of Transportation is reining in SUVs through new corporate average fuel economy (CAFE) standards. By 2011, pickup trucks, minivans, and SUVs will be required to average 24 mpg versus the 21.6 mpg required today.

Plastics makers have to adjust to the decreased demand for SUVs. Chad Waldschmidt, North American director for engineering plastics at Rhodia, has noticed this trend trickle down to engineering plastics suppliers. He has seen his sales to the tier-one suppliers—the parts firms in the supply chain closest to the car company's assembly line—move away from products destined for larger SUVs. "Overall, we are seeing a trend away from some of these vehicles and into smaller vehicles," he says.

But plastics makers also see opportunity in the new attention to fuel efficiency. George Hamilton, president of Dow Automotive, says the car industry is becoming more interested in the potential of plastics to trim vehicle weight. "Until gas got to be about $2.50 per gal, there was more interest in productivity and cost reductions," he says. "But since gas has gone beyond the $2.50-per-gal mark, we find more and more people interested in having discussions about how to lightweight the vehicle and make it more fuel efficient."

Ford's Mielewski confirms that car companies are increasingly looking to plastics. "We are at the point in time when automotive companies will be increasingly pressured to find lightweight technologies that will support improved fuel economy," she says. "Plastic materials for various applications are one way to achieve these improvements."

Howard Cox, lab group manager for composites processes and materials at General Motors, agrees that plastics play a part in car companies' fuel efficiency strategy. "But," he adds, "there is an opportunity for other materials as well, such as advanced high-strength steel, aluminum, magnesium, and composites."

General Motors Photo

Big Red The Hummer H3 has front and rear fenders made from Noryl GTX resin.