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Low-density polyethylene (LDPE) is a thermoplastic made from the monomer ethylene. It was the first grade of polyethylene, produced in ***3 by Imperial Chemical Industries (ICI) using a high pressure process via free radical polymerization. Its manufacture employs the same method today. LDPE is commonly recycled[citation needed] and has the number "4" as its recycling symbol. Despite competition from more modern polymers, LDPE continues to be an important plastic grade.

LDPE is defined by a density range of 0.**0–0.**0 g/cm3. It is not reactive at room temperatures, except by strong oxidizing agents, and some solvents cause swelling. It can withstand temperatures of *0 °C continuously and *5 °C for a short time. Made in translucent or opaque variations, it is quite flexible, and tough but breakable.[citation needed]

LDPE has more branching (on about 2% of the carbon atoms) than HDPE, so its intermolecular forces (instantaneous-dipole induced-dipole attraction) are weaker, its tensile strength is lower, and its resilience is higher. Also, since its molecules are less tightly packed and less crystalline because of the side branches, its density is lower. LDPE contains the chemical elements carbon and hydrogen.

LDPE is widely used for manufacturing various containers, dispensing bottles, wash bottles, tubing, plastic bags for computer components, and various molded laboratory equipment. Its most common use is in plastic bags. Other products made from it include:
Trays and general purpose containers
Corrosion-resistant work surfaces
Parts that need to be weldable and machinable
Parts that require flexibility, for which it serves very well
Very soft and pliable parts such as snap-on lids
Six pack rings
Juice and milk cartons are made of liquid packaging board, a laminate of paperboard and LDPE (as the water-proof inner and outer layer), and often with of a layer of aluminum foil (thus becoming aseptic packaging).
Parts of computer hardware, such as hard disk drives, screen cards, and optical disc drives
Playground slides
Plastic wraps