Asked about the closing, the Dart spokeswoman Becky Warren said in a statement, “We invest our recycling resources in communities that support our customers and our company.”

To Ms. Wayner and others, the move showed that Dart considered polystyrene recycling not a viable enterprise but rather a bargaining chip to ward off regulation.

“As soon as they lost, it was like they took their marbles and went home,” said Martha Ainsworth, a volunteer leader with the Sierra Club in Maryland.

Even with the foam ban, Baltimore faces challenges in achieving its sustainability goals. The Baltimore schools now serve lunch on compostable trays. But there are no facilities in the city that can compost material commercially, so the trays are sent to landfills or an incinerator, according to a spokeswoman for the city school system.

Dart executives say many of their customers also want more sustainable containers, but are facing the financial realities. Some food and beverage companies, they said, want containers made from more recycled and compostable material, but not everyone is willing to accept the additional costs.

Last year, the company opened a laboratory in Mason, where chemists wearing white lab coats and blue rubber gloves hover over beakers and reactors. In one room, technicians tested new coatings for paper coffee cups that are not made of plastic. In another, they analyzed soil samples to test how quickly a compostable cup breaks down.

It’s not clear how long it will take before some of these experiments result in marketable products, but Mr. Lammers said that “it is close.”

“I guarantee you we are going to be different 10 years from now,’’ he said.

