This plastic handle from a kitchen utensil has been deformed by heat and partially melted

One important classification of plastics is the degree to which the chemical processes used to make them are reversible or not.

For thermosetting materials the process is slightly different, as the plastics are liquid to begin with and but must be cured to give solid products, but much of the equipment is broadly similar.

A huge number of plastics exist beyond the commodity plastics, with many having exceptional properties.

High-performance plastics are usually expensive, with their use limited to specialised applications which make use of their superior properties.

A communication campaign infographic showing that there will be more plastic in the oceans than fish by 2050

Because the chemical structure of most plastics renders them durable, they are resistant to many natural degradation processes. Much of this material may persist for centuries or longer, given the demonstrated persistence of structurally similar natural materials such as amber.

Microplastics in sediments from four rivers in Germany. Note the diverse shapes indicated by white arrowheads. (The white bars represent 1 mm for scale.)
Photodegraded Plastic Straw. A light touch breaks larger straw into microplastics.

Microbial species capable of degrading plastics are known to science, some of which are potentially useful for disposal of certain classes of plastic waste.