Terminology

• HDPE: high-density polyethylene, 0.941 g/cm3 or greater
• MDPE: medium-density, 0.926 to 0.940 g/cm3
• LDPE / LLDPE: low-density, 0.910 to 0.940 g/cm3; linear low-density, 0.915 to 0.925 g/cm3
• UHMWPE: ultra-high-molecular-weight, 0.930 to 0.935 g/cm3
• PEX: cross-linked polyethylene
• PE-Xa / Xb / Xc / Xd: peroxide, silane, electron-beam, and azo cross-linking methods

History and demand

Invention

• 1898: Hans von Pechmann first synthesized polyethylene by accident
• 1933: Fawcett and Gibson at ICI rediscovered it; industrial LDPE production began in 1939
• 1951: Phillips Petroleum chromium trioxide catalyst; 1953 Ziegler titanium halide catalyst

Sourcing

• 2024 production: the United States 17 million tons, China 11 million, Saudi Arabia 8.7 million, about 47 percent of 76 million tons (IndexBox)
• Installed capacity: China about 42 million tonnes a year, North America 34, Middle East 23, Western Europe 14 (McKinsey)
• All plastics: 430.9 million tonnes in 2024, with Europe 12 percent and Asia about 55 percent (Plastics Europe)

Demand trend

• 2017: over 100 million tonnes per year, about 34 percent of the plastics market

Composition and production

Raw materials

• Ethylene polymerized by high-pressure, Ziegler-Natta, chromium, or metallocene catalysts

Properties

Physical

• Density: 0.880 g/cm3 (VLDPE) to 0.941 g/cm3 and above (HDPE); about 55 to 59 lb/ft3
• Melting point: 115 to 135°C (239 to 275°F); MDPE and HDPE 120 to 130°C; average commercial LDPE 105 to 115°C

Fire behavior

• Burns slowly with a blue flame and yellow tip, keeps burning after the flame is removed, and drips

Durability

• Yellows as it ages
• PEX: improved high-temperature performance, reduced flow, and enhanced chemical resistance

Uses in buildings

Building elements

• Domestic Water Piping: HDPE water pipe and PEX tubing
• MDPE is used for gas pipe and fittings

Pros and cons

Pros

• PEX tubing expands over a metal fitting and returns to shape, forming a watertight joint
• Cross-linking raises temperature performance

Cons

• Burns and drips
• Yellows with age

Manufacturing and cost

Main manufacturers and suppliers

• Uponor
• Zurn
• Viega

Trade association: Plastics Pipe Institute.

Sources

• Wikipedia: Polyethylene, https://en.wikipedia.org/wiki/Polyethylene
• Wikimedia Commons: Polyethylene balls1.jpg, photo by Lluis tgn (CC BY-SA 3.0), https://commons.wikimedia.org/wiki/File:Polyethylene_balls1.jpg
• IndexBox: polyethylene in primary forms, world market overview 2024, https://www.indexbox.io/blog/polyethylene-in-primary-forms-world-market-overview-2024-13/
• McKinsey Global Institute: polyethylene, widely produced but not one size fits all, https://www.mckinsey.com/mgi/our-research/polyethylene-widely-produced-but-not-one-size-fits-all
• Plastics Europe: plastics, the fast facts 2025, https://plasticseurope.org/de/wp-content/uploads/sites/3/2025/10/PE_TheFacts_25_digital-A4.pdf