High-density polyethylene (HDPE) is a polyethylene thermoplastic made from petroleum. It takes 1.75 kilograms of petroleum (in terms of energy and raw materials) to make one kilogram of HDPE. HDPE is commonly recycled, and has the number "2" as its recycling symbol.
The mass density of High-density Polyethylene can range from 0.945 to 0.960 g/cm³. Although the density of HDPE is only marginally higher than that of Low-density-polyethylene, HDPE has little branching, giving it stronger intermolecular forces and tensile strength than LDPE. The difference in strength exceeds the difference in density, giving HDPE a higher specific strength. It is also harder and more opaque and can withstand somewhat higher temperatures (120 °, cannot withstand normally-required autoclaving conditions. The lack of branching is ensured by an appropriate choice of catalyst and reaction conditions. HDPE contains the chemical elements carbon and hydrogen.
HDPE piping is most commonly used in water and sanitation industry, irrigation system, natural gas network, fire fighting system, transmission lines of foods, supply electric and telephone lines, supply lines under channel, railway and airport runways, and systems used in the injection water from oil wells.