Biodegradable plastic products offer the possibility of relieving consumers of guilt and manufacturers of the responsibilities associated with growing landfills and garbage-choked oceans. According to the U.S. Environmental Protection Agency, only 6.9 percent of plastics were recycled in the United States in 2006, partly because many plastics are composites of different materials and are hard to recycle.

In addition, consumers have recently become more aware of how many products are oil-based, said Steve Davies, marketing director of NatureWorks, a company that makes a bioplastic from plants. With oil prices up sharply, "it's now obvious to just about everybody that our overdependence on oil is bad for our environment, bad for our economy."

The term bioplastics actually has two meanings: sometimes it is used to refer to plastics that contain a percentage of renewable materials; and sometimes to plastics that are both made from renewable materials and are biodegradable.

This ambiguity--and the fact that some bioplastics may also contain petroleum-based polymers--can cloud the green pedigree of a product.

Meanwhile, studies show that consumers are also confused about terms like "renewable" and "biodegradable." "Consumers believe that if it's renewable, then it's inherently good and it's inherently biodegradable," said Steve Mojo, executive director of the Biodegradable Products Institute, an advocacy group. "They also believe that biodegradation is a magical process that will make things disappear."

In fact, biodegradable means susceptible to degradation by microorganisms. But nothing actually breaks down in landfills. Modern landfills are, by design, hermetically sealed tombs for waste.

Nor will biodegradable products necessarily break down if tossed on the side of the road or buried in a backyard. A less confusing term is compostable, which means a product that can be returned to the soil in a beneficial manner.

"Compostable tells a consumer what to do with it," Mojo said, "whereas biodegradable doesn't."

Manufacturers can label products sold in the United States as compostable if they meet standards set by the American Society for Testing and Materials.

Eugene Stevens, a member of the society and a chemistry professor at the State University of New York at Binghamton, has conducted research on biopolymers for more than 30 years. "It's a little complicated, but in general, if it biodegrades to 90 percent within six months in an industrial composting environment with no toxic components, that's compostable," he said.

Europe has a similar protocol.

There are currently three main types of bioplastics, all derived from plant-based starch, which in the United States is typically cornstarch. Vegetable oil or animal fat can also be used to produce polymers that can be substituted for petroleum-based polymers in starch blends to increase overall bio-based content, Mojo said.

Bioplastics manufacturers also are researching the possibility of using cellulose as a feedstock. As in the search for biofuels, cellulose offers the prospect of an abundant supply that could be harvested without chopping down forests or diverting crops and arable land from food production.

But cellulose-based methods, which use acid hydrolysis or enzyme processes, still have technical and cost problems to resolve that have blocked their development on a commercial scale.

The most recent advances try to combine acid hydrolysis and enzyme digestion into a single process; but commercial success is probably still 5 to 10 years away, Stevens said. "Whoever finds the answer to that will be very, very rich," he said. "That is the holy grail."

NatureWorks, a joint venture between Cargill, the U.S. agribusiness giant, and the Japanese chemical company Teijin, manufactures pellets of polylactic acid, or PLA, one of the three main starch-based bioplastics.

PLA can be used to make flexible packaging for fresh foods and beverages like water, milk or orange juice, and to make protective film for wrapping fresh vegetables and flowers. It can also be processed into more rigid products like disposable knives, forks and plates, or hard plastics for cellphone or laptop casings. PLA fibers can also be manufactured for clothing, home textiles, diapers or personal hygiene wipes.

Davies, the marketing director of NatureWorks, said that most manufacturers would be able to modify existing plants to process PLA, rather than having to invest in new equipment. But he also said that the end product had to sell on its merits, like any other.