High-density polyethylene (HDPE), also called polyethylene high-density (PEHD), is a thermoplastic polymer made from the monomer ethylene. When used for HDPE pipes, it is sometimes called "alkathene" or "polythene." With a high strength-to-density ratio, High-density polyethylene (HDPE) is used to produce corrosion-resistant piping. In addition, HDPE is commonly recycled.