The world of plastic contains many confusing terms, as we discovered while reporting on and researching the topic for our June issue of National Geographic magazine. Even the most well-intentioned plastic consumer may have a hard time sorting out “good” plastics from bad. So we’ve prepared a short glossary to help demystify some of the terminology.

Chemicals added during the manufacture of plastic products to make them stronger, safer, more or less flexible, and impart a range of other desired characteristics are known as additives. Common additives include water repellents, flame retardants, stiffeners, softeners, pigments, and UV inhibitors. Some of these additives may contain potentially toxic substances.

A biodegradable product should break down into natural raw materials by microorganisms within