Polyethylene (PE) is a thermoplastic polymer that is widely used in a variety of applications due to its excellent physical and chemical properties and its low cost. It is a polymer made from ethylene monomer units and is produced in several different forms, including low-density polyethylene (LDPE), high-density polyethylene (HDPE), and ultra-high-molecular-weight polyethylene (UHMWPE). LDPE is a flexible and transparent plastic that is used in packaging, tubing, and various household items. HDPE is a stronger and more rigid plastic that is used in applications such as water pipes, fuel tanks, and plastic lumber. UHMWPE is a very strong and durable plastic that is used in applications such as body armor, bearings, and medical implants. Polyethylene can be produced through radical polymerization, but this route has only limited utility and typically requires high-pressure apparatus. Polyethylene is mainly produced via coordination polymerization using Ziegler-Natta or Phillips catalysts.