Air-permeability values for glass veil can be compared only after the test method, pressure differential, reported unit, specimen build and conditioning have been checked. Converting one unit into another changes the notation, but it does not make results from different methods or test conditions directly comparable.
For a board manufacturer, the practical question is not “Which number is lower?” It is “Do these numbers describe the same measurement question, and are they relevant to the facer and board route under review?”
Answer first
- Record the test method and pressure differential before comparing any values.
- Confirm whether the result applies to a loose veil, a coated facer, a laminated sample or a finished board specimen.
- Convert units only after the measurement basis and test area are understood.
- Treat unmatched data as separate evidence, not as a ranked performance table.
Why similar-looking values can answer different questions
Airflow data may be reported as a volume passing through a defined area over time, as resistance to airflow, or through another method-specific expression. The reported number depends on the apparatus, pressure condition, exposed area, specimen mounting, conditioning and calculation used by the test method.
A result from a loose glass veil cannot automatically stand in for a coated or laminated facer. Coating weight, binder, surface treatment, compression and the supporting board can change the measured response. The same caution applies when comparing an acoustic-facing route with a tight-facing route for PIR/PUR boards.
Build a comparability record before using the data
| Field | What to capture | Why it matters |
|---|---|---|
| Method | Method name, procedure or laboratory reference | Different apparatus and calculations may produce results that cannot be ranked directly. |
| Pressure | Specified pressure differential and its unit | Airflow changes with the driving pressure. |
| Reported unit | Full unit, time basis and area basis | A bare number has no usable comparison meaning. |
| Specimen | Loose veil, coated facer, laminated sample or board build | Construction changes the measurement boundary. |
| Conditioning | Temperature, humidity and pre-test preparation when provided | Conditioning differences can affect the result. |
| Replicates | Number of specimens and reported variation | A single reading may not represent roll or lot variability. |
Use unit conversion carefully
Unit conversion is useful when two results already share the same physical basis. For example, a reviewer may convert time or area units so two reports can be read on one worksheet. That calculation should preserve the original value, original unit and conversion formula in the review record.
Conversion cannot repair a method mismatch. Results taken at different pressures, with different exposed areas, or from different specimen constructions remain method-specific even when they are displayed in the same unit. A responsible comparison labels those rows “not directly comparable” until a common test plan is available.
Separate the facer question from the board question
Air permeability can help screen a facer direction, but it does not determine acoustic absorption, foam-board thermal performance, fire behavior or finished-board compliance. Those outcomes belong to the complete construction and its relevant evidence.
For acoustic applications, review airflow together with surface hiding, the acoustic core, adhesive and board construction. The Acoustic Ceiling & Wall Facers solution hub outlines the application context, while the existing guide on airflow, surface hiding and document review explains why one facer property should not be used as a finished-panel promise.
For PIR/PUR boards, a tighter airflow direction still needs to be reviewed with the lamination process and board trial. The guide to ultra-low-airflow glass facer review criteria keeps that boundary clear.
A practical comparison workflow
- Copy the result exactly as issued, including method, unit and pressure.
- Describe the specimen and whether it was loose, coated or part of a board build.
- Mark which fields match across the reports.
- Convert units only for rows with a shared measurement basis.
- Place unmatched rows in a separate evidence group.
- If the decision matters to a trial, agree one test method and specimen build for the next comparison.
Questions to send with a data request
- Which facer route and board application are under review?
- Is the buyer comparing supplier data, incoming material or a trial specimen?
- Which method, pressure and unit does the buyer’s existing data use?
- Does the next decision concern screening, process fit or formal board validation?
FAQ
Can two air-permeability values be compared after converting the units?
Only if the underlying method, pressure, area basis, specimen construction and conditioning are comparable. Unit conversion alone is not enough.
Does lower air permeability mean better board performance?
No. A lower value describes one measured characteristic under stated conditions. Suitability depends on the application, process and finished board system.
What should be done when reports use different methods?
Keep the results in separate evidence groups. If a direct comparison is needed, create a common test plan with the same method, pressure, specimen build and conditioning.
Next step
If your team is trying to reconcile air-permeability reports, contact GRECHO with the original method, pressure, unit, specimen description and board application. GRECHO can help organize the facer route and sample discussion within the available evidence boundary.
