Polyethylene terephthalate (aka PET, PETE, PETP) is a plastic resin used to make beverage, food and other liquid containers, as well as for some other thermoforming applications.
It exists both in as an amorphous (transparent) and as a semi-crystalline (opaque and white) material.
PET was patented in 1941 by the Calico Printer's Association of Manchester.
