DETROIT - From concept cars partially made of discarded soft-drink bottles to plant-based material used in seats and upholstery, automakers are looking at ways to make their vehicles more environmentally friendly.

While efforts to increase fuel economy and cut tailpipe emissions get much of the attention, what goes into making cars is another key part of efforts to green the auto industry.

"The whole issue around sustainability is not just about fuel economy," Mark Fields, Ford Motor Co.'s president for the Americas, said at the North American International Auto Show. "It's not just about lowering CO2 levels. It's being good stewards in the environment, and that means the materials that you use."

The Lincoln MKT, made partly of recycled plastic bottles and polyester waste, underscores Ford's hope to commercialize greener materials and appeal to environmentally minded drivers. It's part of increasing attention industrywide to the overall environmental impact of vehicles.

But unlike Toyota Motor Corp.'s hybrid Prius, which offers drivers instant recognition for buying an environmentally friendly vehicle, car bodies made of recycled materials and interiors that feature plant-based fabrics aren't easily noticeable to buyers.

"It's an open question whether people are willing to pay more," said Jack Nerad, executive market analyst for Kelley Blue Book, who noted such offerings typically come at a premium. "A lot of people want this kind of thing, as they want better fuel economy, but they are not willing to pay more."

It may be more difficult than selling a hybrid, but Nerad said automakers should be able to market these materials to buyers.

"Prius makes a statement about the people who drive them," Nerad said, "so there is this brand opportunity as people are more aware."

Taking steps to make vehicles more environmentally friendly is a given across the industry, auto analysts say. "It's expected that you're making every single effort in every single line to be green," said Aaron Bragman of consulting firm Global Insight.

At the Detroit auto show, Honda Motor Co.'s FCX Clarity hydrogen fuel-cell-powered car uses plant-based fabric for its interior. At the display for Daimler AG's Mercedes-Benz, the automaker highlights that some of its vehicles were awarded an environmental certification for factors including components made from recycled materials.

And Johnson Controls Inc. showed off its new Ecobond headliner that uses soy-based material and natural fibres instead of the traditional fibreglass. The Ecobond ceiling material also cuts weight.

"This approach can help increase fuel economy and reduce carbon emissions," said Jeff Williams, group vice-president for Johnson Controls. It is also easier to recycle at the end of the vehicle's life.

Johnson Controls sells a soy-based seat foam that it says is being used in 1.6 million vehicles for the 2008 model year. Ford also has a soy-based seat foam in the Mustang sports car, F-150 pickup and Expedition sport utility vehicle, as well as the Lincoln Navigator SUV.

Ford says most automakers use about 15 kilograms of petroleum-based foam per vehicle, and producing soy foam uses less energy and reduces carbon dioxide emissions. The cost, Ford says, is about the same.

The weight-saving material used on the body of the Lincoln MKT also was used by Hyundai Motor Co. for its QarmaQ concept car. Designers say the material, made by SABIC Innovative Plastics, illustrates that styling doesn't have to suffer from environmentally responsibility.

Jeff Gearhart, auto project campaign director for the Ecology Center, a nonprofit activist organization based in Ann Arbor, Mich., said car buyers are paying more attention to the overall environmental impact of vehicles. Gearhart said it's akin to the green building movement, which is gaining momentum with construction changes that might not be easily apparent to those who use the buildings.

Green vehicle components can be a selling point and "we're not convinced that addressing all these issues necessarily costs more money," Gearhart said. "It requires another way of thinking."