PEX Tubing Technical Specifications

Reference data for cross-linked polyethylene (PEX) tubing in copper tube size (CTS): dimensions, pressure and temperature ratings, bend radius, thermal expansion, and which fittings work with which tubing. Figures follow ASTM F876 and ASTM F877 unless noted.

PEX Tubing Dimensions (ASTM F876, CTS)

Inside diameter is calculated from the minimum wall thickness, so actual ID can run slightly tighter.

Pressure & Temperature Ratings

Standard-grade PEX carries a three-point rating. All three apply to the same tubing — the allowable pressure drops as temperature rises.

The rating applies to the tubing. A completed joint is only as strong as the weakest component — fittings, rings and sleeves carry their own ratings, and a system is limited by the lowest of them.

PEX-a vs PEX-b vs PEX-c

The letter refers to how the polyethylene was cross-linked, not to a quality grade. All three meet ASTM F876 and all three are approved for potable water.

Fitting Compatibility

Cold expansion is the one method that is not universal — it relies on the shape memory that only PEX-a has.

Fittings, rings and tools are listed as a system. Mixing a ring from one manufacturer with a fitting from another can void the listing and the warranty, even when the parts physically fit.

Minimum Bend Radius

Measured to the centreline of the tube. Below these radii, use a bend support or a 90° elbow. Manufacturers publish their own figures — PEX-a generally bends tighter than PEX-b.

Thermal Expansion

PEX moves far more than copper with temperature — roughly 1.1 to 1.3 inches per 100 feet for every 10°F of change (coefficient about 1.1 × 10^-4 in/in/°F). Long straight runs need expansion loops, offsets, or slack at the ends; rigidly clamping both ends of a hot run is the classic cause of noise and stress at the fittings.

Oxygen Barrier vs Non-Barrier

Plain PEX lets a small amount of oxygen diffuse through the wall. In an open potable system that is irrelevant — the water is replaced constantly. In a closed hydronic loop with ferrous components (cast iron boiler, steel expansion tank, iron circulator volute), that oxygen corrodes the system from the inside.

• Barrier PEX carries an EVOH layer limiting oxygen diffusion per DIN 4726. Required for closed-loop radiant and hydronic heating with any iron or steel in the loop.
• Non-barrier PEX is for potable hot and cold distribution, and for closed loops that are entirely non-ferrous.

Barrier tubing is not approved for potable water unless it also carries a potable listing — check the print line.

Standards & Listings

Handling, UV and Freezing

• UV exposure. PEX degrades in sunlight. Allowable exposure varies by product — commonly 30 to 180 days — and is printed on the tube. Store coils indoors and do not leave a rough-in exposed through a long delay.
• Freezing. PEX expands and generally survives a freeze better than copper or CPVC, but it is not freeze-proof. Fittings are the usual failure point, and repeated freeze cycles accumulate damage.
• Colour coding. Red for hot, blue for cold, white for either. A convention for identification, not a performance difference — the tubing is identical.
• Support spacing. Commonly 32 in on horizontal runs, with vertical runs guided per storey. Spacing is set by your adopted code, so verify locally.
• Burial and slabs. PEX is widely used in slabs and direct burial where approved. Sleeve any penetration through concrete or framing and protect against abrasion.

This page is reference material, not a design document. Values follow published ASTM standards for PEX CTS tubing; individual products vary and manufacturers' submittal data governs. Installation requirements are set by the code adopted in your jurisdiction. Always confirm with the manufacturer's technical literature and your local authority having jurisdiction.