“The Terminator.” “Purple Rain.” “Jeopardy.” Floppy discs. Ronald Reagan. Pagers. “Ghostbusters.” “1984,” the album by Van Halen. All launched in the year 1984. For some of us, it’s hard to believe this was 41 years ago, and while most of the technology of that year has been replaced by devices we could not imagine back then, one of the newer technologies of the time, cross-linked polyethylene, was only getting started. 

In 1984, ASTM F876, Standard Specification for Crosslinked Polyethylene (PEX) Tubing, was first published, beginning the journey for PEX tubing to be introduced into the North American market. This was after more than 10 years of successful use in Europe as a flexible, high-temperature plastic pipe for heating and plumbing systems. 

On the 41st anniversary of this important standard, we look back at the history of PEX tubing in North America and the development of ASTM Standard F876.

Pioneers of PEX

Polyethylene, a combination of multiple ethylene molecules, was first pioneered in the 1930s and developed in the 1940s as an insulation material for radar wiring during World War II. Today, polyethylene is the most widely used type of plastic (i.e., polymer) in the world. 

The idea for cross-linking PE pipe material to improve its temperature resistance and toughness was developed and patented by the German inventor Thomas Engel. He experimented with various technologies before developing a method using the addition of a small amount of peroxide mixed with high-density polyethylene and then extruding that compound through a special extruder capable of generating high pressures and heat. 

This process created cross-linked polyethylene, or PEX. He patented this process in the mid-1960s, but did not own a pipe extrusion facility to put his idea into commercial production. 

In the late 1960s, Engel met with Wirsbo in Sweden (which became Uponor and is now GF Building Flow Solutions) and also with REHAU in Germany and soon licensed his patent to these firms for the production of piping. 

However, according to Tomas Lenman, who joined Wirsbo in 1971: “The patent did not include a ‘ready to go’ production process. Thomas Engel had only been able to produce a few yards at a time. However, these samples proved to be very heat-resistant and did not melt or deteriorate when exposed to temperatures well above the crystalline melting point of more than 130 C (265 F).”

Those two firms, licensing the patent for the so-called “Engel method” of cross-linking, began development of extrusion processes that would allow the PE material to cross-link into PEX during extrusion in a consistent and reliable manner. Both firms started commercial production of PEX tubing for radiant heating applications in 1972. 

Steel pipe and copper tubing had previously been used for radiant heating and snow melting applications up to this point, but with the flexibility, corrosion-resistance and affordability of PEX tubing, the radiant heating market started growing in Europe, delivering higher comfort and efficiency than hydronic wall-mounted radiators. 

In 1982, Lenman traveled to the United States from Sweden with the goal of introducing PEX tubing to this market. He began by contacting the Plastics Pipe Institute to learn about the development process for plastic piping standards. Formed in 1950, PPI, the nonprofit trade association for the North American plastic pipe industry, has always shared technical expertise with industry and helped in the development of industry standards. 

Next, Lenman joined the American Society for Testing and Materials and initiated a project to develop the first ASTM standards for PEX tubing. 

In a recent interview with PPI, Lenman, who was given the nickname “Mr. PEX” by members of the ASTM F17 technical committee, describes the early days of PEX in North America and the development of the foundational product standards. He reports that there was some initial skepticism by manufacturers of other piping materials and building officials within the committee, but Lenman provided the long-term testing reports that had been developed for PEX at the Studsvik Testing Institute (now Element) in Sweden, and these results satisfied the concerns about this “new” material. 

“I rate this as my life’s largest accomplishment!” he says. “The PEX standards were published in 1984, two years after work on it had started.”

These new standards, ASTM F876, Standard Specification for Crosslinked Polyethylene (PEX) Tubing and ASTM F877, Standard Specification for Crosslinked Polyethylene (PEX) Hot- and Cold-Water Distribution Systems, set the stage for code adoption and customer acceptance for PEX tubing systems. ASTM F876 contained the primary requirements for the tubing itself, while ASTM F877 contained performance requirements for fittings to be used as a system with PEX tubing, as well as other requirements specific to tubing used in hot and cold water plumbing systems. 

Thanks to its inherent flexibility, toughness and resistance to high temperatures, the initial applications for PEX tubing in the United States and Canada were in hydronic radiant floor heating and snow and ice melting systems. By 1997, ASTM F876 and F877 had been adopted into several plumbing codes, and PEX began to be used for hot and cold water plumbing systems. Plumbers liked its flexibility and the ability to use home-run style plumbing systems in houses. More code adoptions were achieved and market acceptance followed.

ASTM F876 has continued to evolve to allow for different cross-linking methods (e.g., e-beam was added in 1990, silane was added in 1996), and to add new requirements. For example, mandatory chlorine resistance requirements were added in 2003 and mandatory “outdoor weathering” (i.e., UV resistance) requirements were added in 2020. Chlorine requirements are based on ASTM Test Method F2023, first published in 2000, and UV requirements are based on ASTM Test Method F2657, first published in 2007. 

Successful growth over four decades

Today, PEX systems are approved in all model codes and widely used in plumbing distribution, water service, building supply lines, fire protection, hydronic heating and cooling, radiant heating and cooling, snow and ice melting, turf conditioning, district energy heating and cooling, chilled water, and even certain ground source heat pump systems. 

The North American PEX industry is thriving in both residential and commercial construction, with PEX tubing being the dominant piping material used in residential hot and cold water plumbing, according to HIRL’s Builders Practices Survey report, which showed more than 60% of residential construction using PEX tubing in 2020. 

According to PPI statistical estimates, more than 2 billion pounds of PEX pipe and tubing has been shipped in North America during the past 40 years. Based on traditional tubing size distribution and weight-per-diameter ratios, this translates to more than 30 billion feet of PEX shipped into Canada and the USA since the 1980s. 

PEX has proven to be an exceptionally reliable piping material, delivering safe drinking water and dependable transport of hydronic fluids for heating and cooling systems and numerous other applications for millions of end-users. 

The future of PEX

Since 1984, ASTM Standard Specifications F876 and F877 have provided guidance to manufacturers, certifiers, code officials, system designers, installers and end-users about the capabilities of PEX tubing systems, helping to guide the growth and responsible use of these materials across North America. 

With a strong domestic manufacturing base and international manufacturers — including firms with 30 to 50 years of PEX manufacturing experience — producing according to these ASTM standards and standards from the CSA Group and the American Water Works Association, a tremendous amount of PEX knowledge and expertise is available to users. 

Since the late 1990s, most of these manufacturers have been members of PPI, collaborating to develop research, manuals, software, technical publications and educational tools. 

As the construction of buildings continues to advance, along with customer goals for high-efficiency and sustainable building materials, PEX systems will play an important role in delivering reliable performance, and standards such as ASTM F876 will evolve to lead the way over the next four decades. 

For more information about PEX tubing and systems, including access to the recently published PPI TR-56 History of Crosslinked Polyethylene (PEX) Tubing in North America and the Evolution of ASTM Standard Specification F876 from 1984 – 2024, please visit PPI’s Building & Construction Division at www.plasticpipe.org/buildingconstruction. l

Lance MacNevin, PEng, is the director of engineering for the Plastics Pipe Institute’s Building & Construction Division and has been in the plastic pipe industry since 1993 in various technical roles. He serves on technical committees within ASHRAE, ASPE, ASTM International, AWWA, CSA Group, IAPMO, ICC, IGSHPA, NSF International and RPA, helping to develop codes and piping standards.