High-density polyethylene (HDPE), which is sometimes referred to as polyethylene high-density (PEHD), is an extremely durable type of plastic that has a multitude of uses from food packaging to plumbing pipes. Development of the material started in 1900, but it wasn’t used in a commercial application until 1953 when the British used the plastic to insulate their radar cables. However, HDPE wasn’t formed into a pipe until 1955. Over the last several decades, the pipes have been used for sewer lines, agricultural and industrial plumbing and in potable water applications for cold water lines. HDPE is not used for hot water lines. In buildings where HDPE is used for the plumbing system, PEX is chosen for the hot water lines.
