The most advanced recycling operations in the world divert 75 percent or more of community waste away from landfills. In their efforts to achieve 100 percent recycling, or so-called Zero Waste, three products have proved particularly stubborn:

Diapers

The trouble is twofold: Diapers tend to be made of composite materials, including more than one type of plastic, and there is, of course, the organic waste.

Gary Liss, a recycling consultant in Northern California who sits on the board of several nonprofit recycling groups, including Zero Waste USA, said he knew of one model for recycling diapers, still in the trial stage in Santa Clarita, Calif., that involves separate curbside pickup for used diapers and then the pulling apart and cleaning of the constituent parts. But it’s expensive, Mr. Liss said, and economics are a big part of any recycling equation.

One way to pay for an approach like this would be for diaper manufacturers to include in the diaper’s sales price the cost of picking up used diapers and peeling them apart. But that is unlikely to happen anytime soon.

Mr. Liss said the diaper problem might get worse before it gets better. The reason: baby boomers. “It’s going to be an increasing amount of material as we use adult diapers,” he said. “We’re all headed that way.”