Air Permeability
The volume of air that passes through a fabric under a specified pressure in a given time, reported in litres or cubic metres per square metre per minute.
Weaverine measures air permeability on its own polyester greige — 55–120 GSM, 160–330 cm, woven on 650+ waterjet looms — so the figure on a spec sheet can be traced to a construction the mill runs.
By Wren Thunderborn, Head of Content
Air permeability is the volume of air that passes through a fabric under a specified pressure difference, in a specified time, across a known area. It is reported in litres per square metre per minute (l/m²/min) or in m³/(m²·min), with the test pressure always stated alongside.
It is a property of the fabric as a physical filter. How that translates into comfort is a related but separate question — see the distinction below, which is where most confusion happens.
The standard method
ISO 3795 is the common method. A specimen is clamped in a holder, a pressure difference is applied across it, and the volume of air passing per unit time is measured. The pressure is part of the specification:
| Pressure | Typical use | Notes |
|---|---|---|
| 100 Pa | Often quoted for clothing and general fabrics | The most commonly cited condition in apparel |
| 200 Pa | Also common in textile specifications | Used by several European buyer specs |
| 1,000 Pa | Industrial filtration, technical textiles | Far higher; not comparable with apparel figures |
A figure without its pressure is not a measurement. A fabric that passes 300 l/m²/min at 100 Pa may pass a very different number at 1,000 Pa, and suppliers quote the pressure inconsistently. Always ask for both.
What drives the number
Air permeability is mostly about how open the structure is, and it is the clearest example of a property you can change without changing the fibre:
| Factor | Effect |
|---|---|
| Weave openness | The dominant factor. A plain weave at high ends-and-picks per inch is far less permeable than the same yarn in an open construction |
| Thread count | Higher density = lower permeability, all else equal |
| Fabric weight (GSM) | Heavier fabrics tend to be less permeable, but density matters more than weight alone |
| Yarn twist and hairiness | Hairy, high-twist yarns block the interstices; smooth filament yarns pass more air |
| Finishes | Calendaring compresses the structure and reduces permeability; resin and waterproof finishes can reduce it by an order of magnitude |
| Coatings and laminates | A coated fabric can be close to impermeable regardless of how open the base cloth is |
| Thickness | Thicker cloth adds path length |
Note the tension with weight: a lightweight open weave can be highly permeable while a lightweight tight weave is not, and a heavily finished cloth can be nearly impermeable whatever its base structure. Air permeability is a function of the finished cloth, not the greige.
Air permeability is not "breathability"
These get conflated, and they are different measurements:
| Aspect | Air permeability | Moisture vapour transmission (MVTR) |
|---|---|---|
| Measures | Air passing through the fabric | Water vapour passing through |
| State | Gas / open volume | Vapour / diffusion and evaporation |
| Governs | Air movement, wind, heat exchange | Sweat and comfort in wear |
| Method | ISO 3795 | ISO 11092, ASTM E96 |
A fabric can be highly air-permeable and still perform poorly as a comfort fabric if vapour transport is poor — for instance an open weave in a thick, heavy yarn that moves air but does not wick moisture off the skin. If comfort is the goal, MVTR is the relevant test, not air permeability. Air permeability matters more for filtration, technical applications, and the air exchange people mean when they say a fabric "breathes".
Where it is used
- Technical and industrial textiles — filtration, venting, dust bags, geotextiles
- Apparel — lining and shell fabrics, especially where wind resistance is specified
- Medical — breathability claims and barrier-layer design
- Packaging — materials for air flow and ventilation panels
- Furnishings — where airflow through a curtain or blind affects drape and comfort
For a woven mill this is one of the few specs where weave construction is the whole answer: a buyer asking for a permeability target is really asking you to weave a structure that produces it, and the figure follows from ends-and-picks, yarn, and finish.
What to ask
- What pressure — 100 Pa, 200 Pa, or something else?
- Which method — ISO 3795, and which edition?
- Greige or finished? Finished is almost always the relevant answer, and finishing can dominate the result.
- Warp and weft separately, or an average?
- Conditioned or as-received? See the conditioning note in four-point — it matters here too.
- Is there also an MVTR requirement? If the end use is comfort, ask for both.
Weaving to a target
The practical point for a mill: permeability is designed into the loom, not measured after the fact. Ends and picks per inch, yarn size, and the finishing route together set the figure. That is why it belongs in the specification conversation at the point of choosing the construction — asking a mill to hit a permeability target on a construction already chosen to a different brief is a contradiction, not a request.
Mill greige context
Air permeability is one of the few figures set at the loom, because it follows from ends-and-picks, yarn and the finishing route. On Weaverine greige polyester programs the woven base sits roughly in the 55–120 GSM range at 160–330 cm widths in plain and twill constructions — so a denser construction at the heavier end and an open one at the lighter end will differ substantially before any finish is applied, and finishing can close the gap further.
That is why this belongs in the construction conversation rather than a specification request afterwards. Ask for the structure you need, then ask what it will measure; asking a mill to hit a permeability target on a construction already chosen to a different brief is a contradiction. For the base specification, use the product page.
Weaverine does not publish air permeability figures on this page. The value belongs to a specific construction, weight, finish and test pressure, and a generic number would describe cloth nobody is buying. Ask for the figure against your own construction and test pressure, and check that the supplier states the pressure every time.
Common questions
What is air permeability of fabric?
- Air permeability is the volume of air that passes through a fabric under a specified pressure difference in a specified time across a known area, reported in l/m²/min (or m³/m²·min) with the test pressure always stated. It is a property of the finished cloth as a physical filter, not of the fiber itself.
What is the standard test method for air permeability?
- ISO 3795 is the common method: a specimen is clamped in a holder, a pressure difference is applied, and the volume of air passing per unit time is measured. The test pressure is part of the specification — 100 Pa is the apparel default, 200 Pa is common in European textile specs, and 1,000 Pa is reserved for industrial filtration. A number without its pressure is not a measurement.
Is air permeability the same as breathability?
- No. Air permeability measures air passing through the fabric (open volume, gas state). Breathability in the comfort sense is moisture vapour transmission (MVTR) — water vapour diffusing through the fabric. The two correlate loosely but measure different things. A fabric can be highly air-permeable yet wick poorly (open weave in thick yarn), and a coated waterproof fabric can still pass MVTR. For end uses where comfort matters, ask for MVTR (ISO 11092 or ASTM E96), not air permeability.
What affects air permeability in a woven fabric?
- Weave openness is the dominant factor — the same yarn in a tighter construction is far less permeable than in an open one. Thread count, yarn twist, hairiness, GSM, thickness, and finishing all matter. Calendaring and resin finishes can drop permeability by an order of magnitude; coatings and laminates can take a fabric close to zero regardless of the base cloth. Air permeability is a function of the finished cloth, not the greige.
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