How to Assess Breathability Claims for PU Footwear Materials

A “breathable PU” label is not enough to approve a shoe upper or lining. Ask what was measured, which finished material or assembly was tested, and under which method and conditions. Water vapour passing through a specimen, moisture absorbed by it and air flowing through it are different properties. None alone is a comfort rating for the finished shoe.

This guide is for footwear buyers comparing synthetic PU-coated materials. It explains how to define the evidence needed, not how to run a laboratory test or assign a universal pass level.

Start by naming the property

Water vapour transmission concerns moisture passing through a specimen under the test conditions. Water vapour absorption concerns moisture taken up by the specimen. SATRA TM47 measures both; TM178 focuses on absorption. A strong absorption result should not be presented as proof of strong transmission. (SATRA TM47 public scope; SATRA TM178 public scope)

Air permeability concerns airflow through material under a pressure difference. It is not another name for water vapour permeability. In a laboratory study of PU-finished nonwovens, Jeong and colleagues measured these separately. They reported no detected airflow through the finished artificial leathers at the study’s 125 Pa pressure difference, while also reporting water vapour permeability results. That finding illustrates why the two properties must not be substituted for each other; it does not classify every PU material as impermeable to air. (Jeong et al 2007 full paper)

Liquid-water resistance is a separate question again. SATRA distinguishes water penetration testing from water vapour testing. A vapour result cannot, by itself, substantiate a rain-resistance or waterproof claim. (SATRA preferred test methods 2026)

Use the evidence at the right level

Evidence supplied	What it can help establish	What remains unproven
A backing-only result	The tested substrate’s behaviour	The finished coated material’s behaviour
A finished-sheet result	The identified material under the stated conditions	The same property in the intended layered upper construction
An upper-assembly result	The tested combination of layers	Overall comfort of the complete shoe
A material name or hand-feel description	How the sample is identified or described	A measured breathability result

These are purchasing boundaries, not a hierarchy of guaranteed performance. A test can be useful at each stage if its scope matches the decision being made.

Why the finished construction matters

A test on an uncoated backing is not a substitute for a test on the material you intend to buy. In the study above, six needle-punched nonwoven substrates were finished by laboratory PU dipping and coating. Water vapour permeability decreased after that processing. The study was limited to its particular samples and process; it provides no universal percentage reduction for PU products. Its practical lesson is to verify the finished construction rather than infer its behaviour from the backing alone. (Jeong et al 2007 full paper)

The same discipline applies when a sheet becomes part of an upper. Record the actual layers and how they are combined. SATRA TM47’s public scope includes single materials and assemblies, including synthetics. ISO 17699:2003 covers water vapour permeability and absorption of uppers or complete upper assemblies. A complete upper assembly is not a complete shoe. (SATRA TM47 public scope; ISO 17699 official abstract)

For lining selection, use this evidence alongside the component and assembly questions in our guide to choosing PU materials for shoe linings. Breathability evidence does not replace checks for the other requirements of that component. (PU lining selection guide)

Do not rank unlike reports

Two numbers with the same-looking unit may come from different test conditions. SATRA explains that differences in temperature and humidity gradients between methods can produce different results and even change material rankings. (SATRA preferred test methods 2026)

The purchasing implication is simple: unit conversion alone cannot make unlike tests equivalent. Before ranking candidates, align the method and edition, specimen construction, conditioning, exposure conditions and reported property. Where those do not match, ask the laboratory whether comparison is valid or whether both candidates need testing on the same basis. Do not invent a conversion factor between methods.

For example, suppose one supplier sends a report for a PU sheet and another sends a report for a laminated upper assembly. Even if both reports concern vapour transmission, the comparison mixes material choice with construction choice. First decide which construction your approval concerns. Then obtain evidence for comparable specimens. This is an illustrative purchasing scenario, not a Youxiang test or customer case.

A focused test request

Use the following as a brief for the supplier and testing laboratory, not as a substitute for the full test method.

1. Define the decision. State the shoe component and whether you are screening a finished sheet or approving an upper assembly. Identify the property you need: vapour transmission, vapour absorption, air permeability or liquid-water resistance.

2. Identify the specimen. Record the article code, colour, finish, backing and thickness, plus the layers and bonding arrangement when an assembly is involved. Ask the laboratory to confirm the exposed face and specimen preparation appropriate to the method.

3. Agree the comparison basis. Request the buyer-required method and edition, or ask the laboratory to recommend a suitable method. Agree conditioning and any deviations before testing. Set acceptance criteria with the buyer or brand rather than borrowing a threshold from an unrelated product.

4. Request an interpretable report. Keep the original values and units, specimen identity, test conditions, individual results or variability where reported, deviations and applied acceptance criteria. “Pass” without the requirement is not enough to explain an approval.

5. Limit the conclusion. Record exactly what the evidence supports. If you need a claim about the complete shoe or wearer comfort, agree an additional evaluation with the footwear development team. Do not relabel a sheet or upper-assembly test as that evaluation.

What to say when evidence is missing

If an article has no applicable report, describe its construction and mark the breathability claim as unverified. “Microfiber PU,” “imitation microfiber-backed PU” and “stretch PU” identify sourcing groups; they do not replace article-specific evidence. Our material-structure guide explains why surface, backing and the actual sample should be considered separately from a trade name. (PU material structure guide)

Youxiang Leather is a trading company. This guide does not claim that its materials meet a particular breathability level or have passed the methods discussed. Before a performance claim is used for a selected article, confirm the relevant evidence and intended construction.

The goal is not to find the biggest number. It is to obtain a result that answers the buyer’s actual question, without extending the claim beyond the specimen and conditions tested.

Sources and method limits

Sources were checked on 27 October 2026. The SATRA method pages and ISO abstract are public summaries, not the complete paid methods. They are used here for scope, not detailed procedures, reporting units or pass criteria. Use the applicable full method with the laboratory.

SATRA TM47 public scope. December 2019 revision. Public scope covers absorption and transmission in a single material or assembly, including synthetics.

SATRA TM178 public scope. June 2001 revision. Public scope concerns water vapour absorption; it is not a liquid-immersion absorption test.

Jeong et al 2007 full paper. Jeong et al., 2007. Sen’i Gakkaishi 63(11), 271–275. DOI 10.2115/fiber.63.271. Full five-page paper read; limited laboratory study, not a wearer trial.

SATRA preferred test methods 2026. SATRA Bulletin, January 2026. Used for method-comparison limits and distinction from water penetration testing.

ISO 17699 official abstract. ISO 17699:2003, edition 1, October 2003. Official page reports review and confirmation in 2024. This does not change the designation to 2024.

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