The terms "biodegradable" and "compostable" are defined in official EN, ASTM, and ISO testing standards, but they are not necessarily well understood by the public or even by the plastics industry as a whole. They are often used interchangeably, although they have different definitions.
Compostable plastics, by ASTM and EN definition, must be capable of undergoing biological decomposition at an industrial composting site. In a specified time period, the materials must:
* biodegrade (breaks down into carbon dioxide, water, inorganic compounds and biomass at a rate consistent with other known compostable materials)
* disintegrate (leaves no visible or distinguishable material)
* leave no toxic residue (resulting compost supports plant growth).
What gardeners or US consumers often call composting is better called "backyard" or "home" composting. Some biodegradable or compostable plastics are not compostable in this sense because they will take too long to completely biodegrade. However, composting times can be shorter in a commercial composting facility where materials are shredded and composted under elevated temperatures and humidity.