A sheet of paper can look perfectly uniform and still allow air to pass through it very differently from one batch to the next. That difference matters in packaging, printing, filtration, converting, and any application where porosity affects performance. ISO 5636-5:2013 gives the paper and board industry a recognised way to measure that property using the Gurley apparatus.
This page explains what ISO 5636-5:2013 is, why the Gurley air-permeance test matters, what the method covers, how it differs from related test methods, and where it connects to the work of an inspection body. TNV Inspection Division is a UAF accredited inspection body operating under ISO/IEC 17020:2012, and objective measurement against defined standards is central to how we work.
ISO 5636 is the international series for determining the air permeance of paper and board. Part 5 specifies the Gurley method, a test in which a defined volume of air is forced through a known area of a specimen under a specified pressure difference, and the time taken is measured.
The result helps show how easily air passes through the structure of the paper or board. In practical terms, it gives manufacturers, buyers, laboratories, and inspectors a consistent way to compare material porosity and verify whether a product performs as specified.
Air permeance is not just a laboratory number. It can influence ink holdout, coating behaviour, vacuum feeding, drying, barrier performance, filtration, and the way paper or board runs through converting equipment. A material that is too open or too closed can create production problems even when its thickness and appearance seem correct.
ISO 5636-5:2013 gives that property a repeatable test method. For a manufacturer, it supports process control and batch consistency. For a buyer, it provides a defined acceptance criterion. For an inspector, it creates a common benchmark so findings are based on measured evidence rather than visual judgement alone.
The standard applies to the determination of air permeance of paper and board using the Gurley apparatus. The method is designed for materials through which the specified quantity of air passes within a practical test time and where a reliable seal can be formed around the test area.
The method is most useful when the specimen is sufficiently flat and uniform to prevent edge leakage. Very rough, highly corrugated, exceptionally porous, or easily compressed materials may need another method from the ISO 5636 series or a separately agreed procedure.
The Gurley instrument uses a weighted inner cylinder that moves through a liquid seal and creates a controlled pressure. Once the specimen is clamped over the test opening, the operator records the time required for the selected volume of air to pass through the sheet.
A longer time generally indicates lower air permeance because the sheet resists air flow more strongly. A shorter time generally indicates a more open structure. The test result only has meaning when the instrument, test area, air volume, specimen conditioning, and reporting basis are clearly stated.
Air-permeance testing is sensitive to both the material and the way the test is carried out. The main influences include:
This is why a valid result depends on controlled preparation and competent execution, not simply on placing a sheet in the instrument and reading a stopwatch.
ISO 5636 is a family of methods for the same broad property, but the instruments and reporting approaches are not interchangeable. A few quick relationships:
Results from different methods should not be treated as directly equivalent unless a validated correlation has been established for the particular material. It is also important not to confuse air permeance with surface roughness, water vapour transmission, or gas-barrier testing. Those properties answer different questions and require different standards.
In inspection work, the standard can be used as a defined test criterion when air permeance is part of a purchase specification, technical data sheet, production-control requirement, or customer acceptance plan. The inspection may include sampling, specimen identification, witness of testing, verification of instrument status, review of conditioning records, and comparison of results with the agreed limits.
The distinction is important. ISO 5636-5 describes the test method; it does not by itself set a universal pass or fail value for every paper or board product. The acceptance limit must come from the contract, product specification, regulatory requirement, or another applicable standard. TNV Inspection Division checks the evidence against that agreed criterion and reports what was found.
The standard is relevant to:
● Paper and board manufacturers controlling porosity and production consistency.
● Packaging producers evaluating sheet performance before printing, coating, laminating, or converting.
● Printing and converting businesses investigating feeding, vacuum handling, ink, or coating behaviour.
● Filter-paper, speciality-paper, and technical-paper producers where controlled air flow is a functional property.
● Buyers, laboratories, quality teams, and third-party inspectors verifying material against a stated specification.
If the way air moves through the sheet can affect its intended use, ISO 5636-5:2013 provides a recognised basis for testing it.
This is what separates a real inspection body from a general service provider, so it is worth a moment.
TNV Global Limited (TNV) is accredited by the United Accreditation Foundation (UAF) for inspection, under ISO/IEC 17020:2012 – Conformity assessment – Requirements for bodies providing various types of inspection. We hold that accreditation now, and we keep it through regular surveillance and witnessed inspections.
Our accreditation demonstrates that inspection activities are managed through defined methods, competent personnel, impartial decision-making, controlled records, and reviewed reporting. It also makes the scope and boundaries of every assignment clear before work begins.
In practice, it gives you an independent result supported by a controlled inspection process. The product, lot, sampling basis, test method, acceptance criteria, and inspection stage are agreed in advance. Our inspectors remain separate from the parties whose material they inspect, and our reports state the evidence, limitations, and findings without changing the result to suit a commercial outcome.
For ISO 5636-5 work, that means the reported conclusion can be traced back to identified specimens, test conditions, observed measurements, and the requirement against which those measurements were judged.
An inspection is only as good as the benchmark behind it. Without a defined method, two people could test the same sheet using different areas, pressure conditions, conditioning periods, or reporting units and reach results that cannot be compared.
ISO 5636-5 fixes that problem by defining the Gurley method. It gives the inspection team and the client the same technical language before testing begins. The standard says how the property is determined; the product specification says what result is acceptable; and the inspector independently confirms where the tested material stands.
The process follows our ISO/IEC 17020:2012 framework and stays simple from your side.
TNV Inspection Division is an independent, UAF accredited inspection body working under ISO/IEC 17020:2012. For paper and board inspection, you get qualified personnel, defined sampling and reporting, impartial findings, and a clear connection between the measured result and the specification you need to satisfy. We do not turn a test value into a vague promise; we show what was checked, how it was checked, and what the evidence says.
Need an independent, accredited partner for paper or board inspection and Gurley air-permeance verification? Contact TNV Inspection Division for a clear scope and a free quote.
