This is genuine recycling, whereas most other materials are selected and purchased, not found on the street. (airgallery.org)
Most other materials biodegrade or are not as buoyant as plastics, which do not biodegrade. (discovermagazine.com)
It is suitable because its nuclei give off signals with a very narrow range of frequencies, only about 4 hertz, compared to thousands of hertz for most other materials. (newscientist.com)