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Low-Density Polyethylene (LDPE) is a thermoplastic made from the ethylene monomer and is recognized as the oldest member of the polyethylene (PE) family. Its discovery dates back to 1933, when Imperial Chemical Industries (ICI) scientists in England, including Eric Fawcett and Reginald Gibson, accidentally produced a white, waxy solid during high-pressure experiments with ethylene. This early synthesis required extremely high pressures and was initially difficult to reproduce until Michael Perrin, another ICI chemist, developed a reliable high-pressure process by 1935. ICI was granted a patent for the process in 1937, and commercial production of LDPE began in 1939.

The onset of World War II quickly highlighted LDPE's value: its excellent insulating properties made it indispensable for applications such as radar cable insulation and submarine cables, where it replaced natural materials like gutta-percha. The use of LDPE in military technology was considered so critical that its production methods were kept secret during the war.

LDPE's unique structure—characterized by significant branching—distinguishes it from later forms of polyethylene, such as high-density polyethylene (HDPE), which was developed in the 1950s using new catalyst-based processes. Despite the emergence of newer polymers, LDPE remains an important material in the plastics industry due to its flexibility, chemical resistance, and ease of processing.

The free-radical, non-catalytic high-pressure polymerisation process employed in the production of LDPE results in a highly branched molecular structure, in its turn responsible for the low density of the product. This branching reduces intermolecular forces, making LDPE less crystalline and more flexible compared to other polyethylene types like HDPE.

LDPE is produced in a density range of 917–930 kg/m³ with a melting point between 110°C and 115°C (230°F and 239°F), and a melt index ranging from 0.2 g/10 min-70 g/10 min, depending on the application. It has the SPI recycling code nr. 4.