Recycling levels for polypropylene, or No. 5 plastic, have improved even as many major U.S. cities do not collect the material. "[No. 5 plastics] are not mainstream, but that's because it takes a while for things to catch on," said Judith Dunbar, the American Chemistry Council's director of environmental and technical issues for plastics. "It's really a volume issue just like anything else. If you don't have a lot of volume, then it's not going to sell," Dunbar added.