Editing Polyethylene (section)

===High-density (HDPE)===
{{main|High-density polyethylene}}
[[File:Site Photo of HDPE Pipe.jpg|thumb|HDPE pipe on site during installation in outback Western Australia. The white outer layer, Acu-Therm, is co-extruded to provide a reduction of thermal heating.]]
HDPE is defined by a density of greater or equal to 0.941&nbsp;g/cm<sup>3</sup>. HDPE has a low degree of branching. The mostly linear molecules pack together well, so intermolecular forces are stronger than in highly branched polymers. HDPE can be produced by [[chromium]]/silica catalysts, [[Ziegler–Natta catalyst]]s or [[metallocene]] catalysts; by choosing catalysts and reaction conditions, the small amount of branching that does occur can be controlled. These catalysts prefer the formation of [[free radicals]] at the ends of the growing polyethylene molecules. They cause new ethylene monomers to add to the ends of the molecules, rather than along the middle, causing the growth of a linear chain.

HDPE has high tensile strength. It is used in products and packaging such as milk jugs, detergent bottles, butter tubs, garbage containers, and [[HDPE pipe|water pipes]].