For all their benefits, plastics do present a notable problem: their sheer durability means they persist in the environment for many years, while their lightness means they can be carried great distances, for example as ocean debris. The bodies of fully a quarter of the world's seabirds are estimated to contain some sort of plastic residue. Waste plastics such as PET are now recycled into a range of useful goods, such as upholstery padding and thermal clothing. Unlike other plastics, which are produced from petroleum, polyhydroxybutyrate (PHB), sold as Biopol, is produced as a natural polymer by certain bacteria as a means of storing their energy. It breaks down harmlessly in soil, but is much more expensive than other plastics. You can read more about environmentally friendly plastics in our detailed article about bioplastics .