Polylactic acid, also known as poly(lactic acid) or polylactide (PLA), is a thermoplastic polyester with backbone formula. PLA has become a popular material due to it being economically produced from renewable resources. In 2010, PLA had the second highest consumption volume of any bioplastic of the world,^[3] although it is still not a commodity polymer. Its widespread application has been hindered by numerous physical and processing shortcomings.^[4] PLA is the most widely used plastic filament material in 3D printing. Its low melting point, high strength, low thermal expansion, good layer adhesion, and high heat resistance when annealed make it an ideal material for this purpose. Without annealing, however, PLA has the lowest heat resistance of the common 3D printing plastics.

Although the name “polylactic acid” is widely used, it does not comply with IUPAC standard nomenclature, which is “poly(lactic acid)”.^[5] The name “polylactic acid” is potentially ambiguous or confusing, because PLA is not a polyacid (polyelectrolyte), but rather a polyester.^[6]