When thinking of green vehicles, what tends to come to mind are cars like the GM Volt with electric powertrains. Many carmakers are also looking to use recycled and green parts inside the car's interior. The Detroit News reports that automakers are now using materials like worn out jeans, plastic bottles, and other rubbish typically thrown in the trash.

GM materials engineer Lora Herron said, "If we have two parts -- one is recycled, the other one is virgin -- and they perform and cost the same, why wouldn't you use the recycled one?"

Carmakers often see cost savings in using recycled materials for parts, but not always. It can be hard for the manufacturer to design a part that is as durable as parts made from manmade plastics and materials. That means that the car marker has to spend more time in research and development, which could make the recycled part more expensive.

One of the big recycled items that GM uses in interior parts are recycled plastic milk cartons. Last year 9% of all milk cartons, detergent bottles, and other containers made form high-density polyethylene were used in automotive parts in America. Ten years ago, the percentage was negligible.

Plastic isn't the only recycled material making their way into vehicles today. The 2010 Buick LaCrosse is using cardboard from the GM Marion Stamping Plans as acoustic ceiling panels. GM also uses kenaf for ceiling support and acoustics in some vehicles. Kenaf is a plant similar to bamboo.

Herron estimates that GM uses 5-10% recycled plastics in its vehicles. The manufacturer is even turning scrap yarn from carpet mills into plastic for an engine part in some of its vehicles. Ford also uses recycled plastics in its vehicles as well as biodegradable plastics made from corn and switch grass. "We said hey, we have to do a little better than great gas millage," said Carol Kordich, Ford's lead sustainability designer. "So we started looking into the interior."