There is growing evidence that the production, use and disposal of plastic bags put less burden on natural resources than paper bags. Meanwhile, a knock against plastic bags -- that they can't be conveniently recycled -- is becoming less persuasive as more cities start accepting plastic bags in curbside recycling programs.

That makes the cash-register question -- paper or plastic? -- more vexing than ever. "It depends on what environmental issues you see as being more important," says Lisa Mastny, who directs the consumption project at the Worldwatch Institute, an environmental group. "The things you can see in your daily life tend to create more of an emotional response than the things that are in the background."

A reusable bag is better for the environment regardless of what it is made from, as long as it is used at least four times, according to a 2004 study by the French retailer Carrefour.

the compostable plastic bag

accidentally recycled, it can contaminate the regular plastic