PEX Oxygen Barrier (EVOH): The Number to Specify and How to Verify It

An oxygen barrier is a number, not a feature. On a compliant PEX or PE-RT heating pipe it means oxygen permeation held to 0.32 mg O₂/(m²·day) at 40 °C — and 3.6 mg O₂/(m²·day) at 80 °C — measured by a defined test method. Every other use of the phrase is marketing.

That distinction matters because "oxygen barrier" is printed on product pages that never state the limit, never name the standard, and never show a test result. A distributor comparing two quotes has no way to tell whether both pipes meet the same requirement or whether one supplier simply liked the phrase. This article gives you the number, the standard behind it, the test method that produces it, and the document to demand before a container is built.

What "Oxygen Barrier" Has to Mean on a Purchase Specification

The reason the barrier exists is well established and not the subject of this page: a sealed heating loop recirculates the same water for years, oxygen diffuses through bare polyethylene, and the dissolved oxygen corrodes the ferrous parts sharing the circuit — boiler heat exchangers, pump housings, steel manifolds. We cover that mechanism, and when a system can tolerate non-barrier pipe, in our guide to underfloor heating pipe selection.

What that guide does not do — and what almost no page currently ranking for this term does — is tell you what number you are entitled to demand. That gap is the entire problem for anyone buying pipe rather than installing it.

Consider the position of an importer holding two quotations. Both datasheets say "oxygen barrier EVOH". One pipe is a five-layer PE-RT construction with a third-party report from an accredited laboratory. The other is a single-layer pipe with a thin skin and a supplier's own word. Nothing in the phrase distinguishes them. The price difference is real, the buyer sees it, and without a specification he is choosing on price between two products that are not the same product.

The claim becomes checkable the moment you attach three things

• A limit — the permitted permeation rate, in mg O₂/(m²·day), at a stated temperature.
• A method — the test procedure that produces that figure, including how the sample was conditioned first.
• A document — a report from a named laboratory showing the measured result against the limit.

Attach all three and "oxygen barrier" becomes a contractual term you can reject a shipment against. Attach none and it is a word on a brochure. The rest of this article supplies all three.

The Two Numbers: DIN 4726 and EN ISO 21003-2

The German standard DIN 4726, covering warm-water surface heating and radiator connecting systems, sets the permeation limit that the European market works to. It is expressed per unit of pipe surface area, per day, at a stated water temperature:

Test temperature	Maximum permitted permeation	Where the same limit appears
40 °C	≤ 0.32 mg O₂/(m²·day)	DIN 4726 and EN ISO 21003-2
80 °C	≤ 3.6 mg O₂/(m²·day)	DIN 4726 and EN ISO 21003-2

The second column of that table is worth dwelling on. Accredited test reports list the DIN 4726 requirement and the EN ISO 21003-2 requirement as separate lines — and both carry the identical figure at 40 °C. So when a supplier's datasheet cites one standard and a competing datasheet cites the other, that is not a difference in stringency. It is the same threshold under two references, and a buyer who treats one as superior is inventing a distinction that does not exist.

The stale figure that will cost you an unverifiable spec

Search this topic and you will still find the requirement quoted as "0.1 grams per m³ per day at 50 °C". It is a legacy volumetric statement of the same intent, and it is repeated on trade sites today. The problem is not that it is historically wrong — it is that no laboratory reports against it. Accredited reports and manufacturer catalogues alike state results in mg per square metre per day, at 40 °C or 80 °C.

A Limit Without a Test Method Is Not a Specification

The permeation figure is produced by ISO 17455 — "Plastics piping systems — Multilayer pipes — Determination of the oxygen permeability of the barrier pipe". Published in 2005, carrying a 2007 corrigendum, and reviewed and confirmed as current in 2021. It defines two approaches, a dynamic and a static method; accredited reports on heating pipe typically use the dynamic method, designated method I.

The test parameters are specific enough to be quoted back at a supplier. A representative accredited test runs at a controlled 40 °C ± 0.5, on a free pipe length of 20 m ± 0.5 with no fittings in the assembly, with an oxygen detection limit of 0.1 µg O₂/l. Results are recorded across several runs and averaged.

The 28-day step almost nobody mentions

Here is the part that separates a real conformity test from a convenient one. Before the permeation measurement, DIN 4726 requires the sample to be pre-conditioned in three stages:

1. Bending — the pipe is bent to 8 × the nominal diameter across 10% of the assembly length, then held in air at 23 °C ± 2 for 24 hours. This stresses the barrier layer the way a real installation does.
2. Water conditioning — water in water at 20 °C ± 1 for 24 hours.
3. Drying — water in air at 23 °C ± 2 and 50% ± 5 relative humidity, for 28 days.

EVOH is hygroscopic. Its barrier performance is sensitive to moisture, and a sample tested straight off the line, still wet, does not behave the way pipe in a warehouse behaves. The 28-day drying stage exists to remove that advantage. It is also why a genuine conformity test takes over a month of calendar time before the measurement even begins — which tells you something useful about any supplier who offers to produce one by Friday.

Practically: when a datasheet claims DIN 4726 compliance, the meaningful question is not whether the pipe passed, but whether the sample went through this conditioning. Ask for the report, and look for the pre-conditioning section.

Where the EVOH Actually Sits — and Why the Datasheet Wording Matters

A widely-copied description of barrier PEX calls EVOH an "external coating of special polymer". For some products that is accurate. For the constructions most commonly sold into heating projects it is not, and the difference has practical consequences on site.

Two constructions dominate, and manufacturers document them precisely:

Construction	Layer stack, inside to outside	Where EVOH sits
4-layer barrier PEX	Cross-linked HDPE · adhesive · EVOH · thin outer PE skin	Third layer, protected by an outer skin
5-layer barrier PE-RT	PE-RT · adhesive · EVOH · adhesive · PE-RT	Middle of the wall, tied both sides

In the four-layer form, the outermost material is a thin polyethylene layer whose stated job is to protect the EVOH from damage. In the five-layer form, the EVOH sits at the centre of the wall between two adhesive tie layers of maleic-anhydride-modified polymer. Neither is a surface coating in the ordinary sense.

The standards allow both. ASTM F3253 defines its scope around tubing incorporating "a single outer or middle wall oxygen barrier layer" — so a datasheet describing an outer barrier liner is not necessarily non-compliant. It is describing a different product.

Read the tie layers, not the adjectives

A datasheet that names its adhesive layers is describing a real extrusion process. One that says only "with EVOH oxygen barrier" may be describing anything. When you request a technical datasheet, the useful detail is the layer count and what each layer is made of — that single paragraph tells you more about the product than the entire marketing section above it.

What a Real Conformity Document Looks Like

This is the part a buyer can act on immediately. Below are two genuine oxygen-permeability reports issued by Kiwa Nederland, an accredited European testing body, on two different manufacturers' pipe — report LC 21574-1 (PDF) and report LC 14439 (PDF). Neither is IFAN's pipe — they are published third-party documents, shown here because they demonstrate what a credible report contains and what real results look like.

Report	Product tested	Requirement	Measured
Kiwa LC 21574-1, 27-07-2022	PE-RT type II / EVOH / PE-RT type II, 16 × 2.0 mm	≤ 0.32 mg O₂/(m²·day) at 40 °C	< 0.03 mg O₂/(m²·day)
Kiwa LC 14439, 26-07-2017	PE-Xa / EVOH, 16 × 2.2 mm	≤ 3.6 mg O₂/(m²·day) at 80 °C	0.25 mg O₂/(m²·day)

Read the margins, because they are the most instructive figures on this page. The PE-RT sample came in below 0.03 against a limit of 0.32 — better than a factor of ten. The PEX-a sample measured 0.25 against a limit of 3.6 at the harsher 80 °C condition. A working EVOH barrier does not scrape past the requirement; it makes the requirement look generous.

That gives you a practical heuristic. A reported result sitting just beneath the limit — 0.28 against 0.32, say — is not a pass to celebrate. It is a result worth asking about, because a properly constructed barrier should not be operating that close to the edge. Ask which pre-conditioning was applied and how many test runs were averaged.

The five things a usable report contains

• A report number and date — traceable, not a screenshot of a table.
• The issuing laboratory — a named accredited body, with the requesting company named too.
• The exact product tested — material construction and nominal dimensions, e.g. "PE-RT type II / EVOH / PE-RT type II, 16 × 2.0 mm". If it does not match your order, it is not your evidence.
• Requirement and measured value side by side, at a stated temperature.
• The pre-conditioning applied — the bending, water and 28-day drying stages described above.

The field-level check: read the print line

A report covers a sample. The print line covers the coil in front of you. A compliant barrier pipe carries its credentials along the pipe itself — here is a real print line transcribed from the sample in report LC 21574-1:

PERT EVOH 16x2,0 PERT Tipo II – C – Oxygen Barrier – Class 1/10 bar – 2/8 bar – 4/8 bar – 5/8 bar – UNE EN ISO 22391 – Made in Spain – Linea 1 – Lo 12/05/22

Note what is encoded there: the construction and size, the material type, the words "Oxygen Barrier", four application class and pressure pairs, the product standard, the country of manufacture, the production line number, and a lot code with a date. On a goods-inwards inspection, the line number and lot code are what let you trace a suspect coil back to a specific production run — and what let you reject a delivery whose print line does not match the pipe you specified.

If You Are Buying for North America: ASTM F3253

DIN 4726 governs the European conversation. North American projects run on an ASTM specification instead, and a distributor serving both markets needs to know they are not interchangeable documents.

ASTM F3253 — "Standard Specification for Crosslinked Polyethylene (PEX) Tubing with Oxygen Barrier for Hot- and Cold-Water Hydronic Distribution Systems" — covers PEX tubing with a polymeric oxygen barrier in a single dimension ratio, SDR 9, for hydronic heating and cooling up to and including a maximum working temperature of 200 °F (93 °C). Its scope explicitly admits either a single outer or middle wall barrier layer, and its test suite covers oxygen permeation and layer adhesion alongside burst pressure, sustained pressure, thermo-cycling, bent tube, oxidative resistance and UV resistance.

Usefully for anyone comparing across regions, manufacturers serving the US market often declare the permeation figure against the same yardstick. One published North American technical datasheet states permeation of less than 4.588 × 10⁻⁴ grains/(ft²·day) at 104 °F — which it then expresses as 0.32 mg/(m²·day) at 40 °C, tested in accordance with ISO 17455. Same number, same method, different units.

Reading a North American print line

A US barrier PEX tube typically carries a pressure rating of 100 PSI at 180 °F and 160 PSI at 73 °F, with the tube built and tested to a suite of standards rather than one: ASTM F876 and F877 for the PEX itself, F3253 for the barrier, F3348 for press insert fittings, and CSA B137.5. Degree of cross-linking is determined by ASTM D2765. A second manufacturer states the same rating in metric — 690 kPa at 82 °C and 1100 kPa at 23 °C — across nominal sizes from 3/8" to 1".

The dual-market implication is straightforward. A pipe certified to EN ISO 22391 with a DIN 4726 barrier report is not automatically acceptable on a US hydronic job, because the US specification chain also wants ASTM F876/F877 dimensional and pressure conformity and, in many jurisdictions, NSF listings. If you sell into both, ask suppliers for both certification chains explicitly rather than assuming one implies the other.

Putting It on the Purchase Order

Everything above reduces to a few lines of text in a tender document. Here is the specification language, written so a supplier can either meet it or decline it — which is exactly what you want a specification to do.

Ordering practicalities, and where IFAN currently stands

On commercial terms, IFAN works to a minimum of one container with mixed sizes permitted, sells strictly B2B wholesale, and ships FCL or LCL with full export documentation. Pricing is quoted against a submitted product list rather than published as a list price, because the number moves with resin cost, size mix and volume — so the honest answer on price structure is that it is built from your size mix, not read off a page. Lead time is confirmed per order at quotation, as it depends on the size mix and current line loading.

On the product itself, a straight answer is more useful than a comfortable one. IFAN's published floor-heating range lists PE-RT coils in 16–32 mm, with two catalogued SKUs at the time of writing: HL106-155 at 16 × 2.0 mm in 100 m coils and HL106-156 at 20 × 2.0 mm in 100 m coils. Our documented certification record covers the PP-R line — DIN 8077/8078, ISO 15874, CE and SGS, with SASO, SONCAP or NOM available on request — and those are PP-R certifications, not PEX or PE-RT ones.

Your next three steps

1. Put the clause above into your RFQ, with the limit, the method and the document request stated explicitly.
2. Ask every quoting supplier for the test report and the layer construction, and compare the tested dimensions against the sizes you are actually ordering.
3. Check the print line on the sample coil before you approve production, and again on arrival.

If you are still deciding between materials before you get to the barrier question, our comparison of PE-RT and PEX for heating circuits covers weldability, temperature classes and installed cost, and the PEX pipe guide covers the PEX-a, PEX-b and PEX-c distinction. For the manifold end of the circuit, where the ferrous components most at risk from oxygen actually live, see our guide to the PEX manifold. Our current PEX and PE-RT range, with the catalogued coil sizes and packing data, sits in the PEX and PE-RT category.

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