Low-density polyethylene (LDPE) is a thermoplastic

Thermoplastic

Thermoplastic, also known as a thermosoftening plastic, is a polymer that turns to a liquid when heated and freezes to a very glassy state when cooled sufficiently...

 made from petroleum

Petroleum

Petroleum or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth's surface. Petroleum is recovered mostly through oil drilling...

. It was the first grade of polyethylene

Polyethylene

Polyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons...

, produced in 1933 by Imperial Chemical Industries

Imperial Chemical Industries

Imperial Chemical Industries was a British chemical company, taken over by AkzoNobel, a Dutch conglomerate, one of the largest chemical producers in the world. In its heyday, ICI was the largest manufacturing company in the British Empire, and commonly regarded as a "bellwether of the British...

 (ICI) using a high pressure process via free radical polymerization

Radical polymerization

Free radical polymerization is a method of polymerization by which a polymer forms by the successive addition of free radical building blocks. Free radicals can be formed via a number of different mechanisms usually involving separate initiator molecules...

. Its manufacture employs the same method today. LDPE is commonly recycled and has the number "4" as its recycling symbol

Resin identification code

The SPI resin identification coding system is a set of symbols placed on plastics to identify the polymer type. It was developed by the Society of the Plastics Industry in 1988, and is used internationally....

. Despite competition from more modern polymers, LDPE continues to be an important plastic grade. In 2009 the worldwide LDPE market reached a volume of US$22.2 billion (15.9 billion Euro).
LDPE is defined by a density range of 0.910–0.940 g/cm³.