PEX Tubing: Definition & Technical Guide
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PEX tubing, short for cross-linked polyethylene tubing, is a flexible plastic piping material used in residential and commercial plumbing for potable water distribution, hydronic radiant heating, and fire sprinkler systems. PEX is manufactured by cross-linking polyethylene molecules to create a durable, heat-resistant, and corrosion-proof material that has become the dominant choice for residential water supply piping in the United States since the early 2000s.
Cross-Linking, Flexibility & Pressure-Temperature Performance
Cross-linking transforms ordinary polyethylene — a thermoplastic that softens when heated — into a thermoset material with a three-dimensional molecular network that maintains its shape and strength under pressure and elevated temperatures. The cross-linked structure gives PEX tubing a maximum working pressure of 100 PSI at 180 degrees Fahrenheit and 160 PSI at 73 degrees Fahrenheit, meeting the demands of residential hot and cold water distribution.
PEX tubing’s flexibility allows it to bend around corners and route through wall cavities with fewer fittings than rigid pipe systems. Fewer fittings means fewer potential leak points and faster installation. A single length of PEX can run from a manifold to a fixture without any intermediate connections, a configuration called “home run” plumbing that also allows individual fixture shutoff at the manifold.
PEX is resistant to scale buildup, pitting corrosion, and the chemical degradation that affects copper in aggressive water conditions. It also dampens water hammer noise more effectively than rigid piping because the flexible tube walls absorb pressure surges. However, PEX cannot be used for outdoor above-ground applications because ultraviolet light degrades the material. It is also not approved for use with gas piping.
PEX-A (Engel), PEX-B (Silane) & PEX-C (Radiation) Types
PEX-A (Engel method) is cross-linked during the extrusion process using peroxide. It has the highest cross-link density (typically above 70 percent), the greatest flexibility, and the unique ability to be used with expansion fittings. PEX-A is the most expensive of the three types.
PEX-B (Silane method) is cross-linked after extrusion using a moisture-cure process. It has a cross-link density of 65 to 70 percent, is slightly stiffer than PEX-A, and works with crimp, clamp, and push-fit connection methods. PEX-B is the most widely used type due to its balance of performance and cost.
PEX-C (Radiation method) is cross-linked after extrusion using electron beam radiation. It has the lowest cross-link density (typically 60 to 65 percent) and is the stiffest of the three types. PEX-C is less common in plumbing but used in some radiant heating applications.
Color coding distinguishes hot and cold lines: red PEX for hot water, blue for cold water, and white for either. The color is cosmetic only — all three colors have identical performance specifications.
Repiping, Home Run Manifolds & New Construction Applications
PEX tubing is the primary piping material Bonded Plumbworks’ plumbers use for repiping projects in homes transitioning from corroded galvanized, polybutylene, or failing copper systems. PEX’s flexibility reduces installation time and cost compared to rigid alternatives, and its corrosion resistance eliminates the pinhole leak failures common in copper piping exposed to aggressive local water chemistry.
Bonded Plumbworks also installs PEX in new construction bathroom plumbing and kitchen plumbing rough-ins, as well as manifold-based home run systems that provide individual fixture control and balanced pressure across all outlets.
ASTM F876, F877 & NSF/ANSI 61 Potable Water Standards
ASTM F876 covers PEX tubing specifications for hot and cold water distribution. ASTM F877 covers PEX tubing systems including fittings and manifolds. The applicable state building codes permits PEX for potable water distribution, with all components required to bear NSF/ANSI 61 certification for potable water contact. PEX must not be exposed to direct sunlight for more than 60 days during construction per manufacturer guidelines. SDR-9 is the standard dimension ratio for most residential PEX plumbing applications.
Uponor, Viega, SharkBite & Zurn PEX Systems
Uponor (formerly Wirsbo) manufactures PEX-A tubing and the ProPEX expansion fitting system. Viega produces PEX tubing compatible with both crimp and press-fit connections. SharkBite offers PEX-B tubing paired with their push-fit connector system. Zurn manufactures PEX-B tubing with crimp and cold expansion connection options.