Introduction

A complete technical guide to air permeability measurement principles, test standards, fabric parameters, and applications across technical textiles, filtration media, medical fabrics, and geotextile quality assessment.

mm/s & cm³/cm²/s
ISO 9237 / ASTM D737
Multi-Layer Testing
Digital Readout
Fison Air Permeability Tester
Precision Fabric Airflow Measurement
±2% Accuracy1–20 cm² Test Area0–5000 mm/s Range

"Air permeability is one of the most functionally significant properties of any textile — it determines thermal comfort in apparel, filtration efficiency in industrial media, breathability in protective clothing, and drainage capacity in geotextiles. Measuring it accurately is the foundation of fabric quality assurance."

Air permeability is defined as the volume flow rate of air per unit area of fabric under a specified differential pressure — typically expressed in mm/s or cm³/cm²/s. It quantifies how freely air passes through a fabric's pore structure, which is determined by fibre type, yarn count, weave or knit architecture, finishing treatments, and fabric weight.

The Fison Air Permeability Tester measures this property by clamping a fabric specimen between test heads, applying a controlled differential pressure across the specimen (typically 100 Pa per ISO 9237 or 125 Pa per ASTM D737), and measuring the resulting airflow rate through the fabric area. Results are displayed digitally and used to accept, reject, or grade fabric lots against specification limits across apparel, industrial, filtration, medical, and geotextile applications.

How Air Permeability Testing Works

Step-by-step measurement process from specimen preparation to reported result

1
Specimen Preparation
Fabric conditioned at 20°C / 65% RH per ISO 139 for 24h. Multiple specimens cut from different positions across fabric width to account for variation
2
Specimen Clamping
Specimen clamped between circular test heads over defined test area (1, 5, 10, or 20 cm²). Clamp pressure prevents air bypass around specimen edges
3
Differential Pressure Applied
100 Pa (ISO 9237) or 125 Pa (ASTM D737) applied across specimen. Fan draws air through fabric at controlled, stable pressure
4
Flow Rate Measurement
Calibrated flow sensor measures volumetric airflow through specimen. Digital display shows result in mm/s, cm³/cm²/s, or cfm per ft²
5
Statistical Reporting
Mean, SD, and CV% calculated across minimum 10 specimens. Result compared to specification — accept, reject, or conditional release decision made
Test Pressure Selection: ISO 9237 specifies 100 Pa as standard for apparel and technical textiles. ASTM D737 uses 125 Pa. For very open structures (nonwovens, geotextiles) lower pressures (50 Pa) may be used. Always match test pressure to the applicable product standard — results at different pressures are not directly comparable.
Fabric Permeability Ranges by Type

Expected air permeability values across major textile and technical fabric categories

0–5000
mm/s
Full Range
Air permeability spans six orders of magnitude across fabric types — from near-impermeable barrier membranes to highly open geotextile grids
Permeability by Fabric Category (mm/s at 100 Pa)
Woven Shirting & Apparel80–300 mm/s
Sportswear & Performance Knits150–600 mm/s
Medical Nonwovens200–800 mm/s
Air Filtration Media (HEPA pre-filter)10–80 mm/s
Geotextiles & Drainage Fabrics1000–5000 mm/s
Barrier & Protective Membranes<5 mm/s
Automotive & Technical Felts400–2000 mm/s
Materials Tested
Woven FabricsKnitted FabricsNonwovensTechnical TextilesGeotextilesFilter MediaProtective FabricsLaminatesMembranesCoated FabricsMedical DrapesAutomotive Felts
Key Performance Features

Six capabilities that define laboratory-grade air permeability measurement instruments

01
±2% Measurement Accuracy

Calibrated flow sensor and precision pressure transducer maintain ±2% accuracy across the full measurement range — traceable to national standards for quality system compliance and inter-laboratory comparison

Accuracy: ±2% of reading
02
Variable Pressure Settings

Test pressure selectable from 20 Pa to 500 Pa — supports ISO 9237 (100 Pa), ASTM D737 (125 Pa), EN ISO 9237, and product-specific test pressures for filtration, geotextile, and automotive specifications

Range: 20–500 Pa selectable
03
Multi-Unit Digital Display

Results displayed simultaneously in mm/s, cm³/cm²/s, L/m²/s, and cfm/ft² — eliminating manual unit conversion errors when comparing results across international standards or customer specifications

Units: 4 simultaneous formats
04
Interchangeable Test Heads

Test area heads in 1, 5, 10, and 20 cm² configurations accommodate different fabric structures — small areas for coarse open weaves, large areas for filtration and nonwoven uniformity assessment per standard requirements

Test Areas: 1 / 5 / 10 / 20 cm²
05
Onboard Statistics

Automatic calculation of mean, standard deviation, minimum, maximum, and CV% across up to 10 readings per test series — generates QC-ready statistical summary without manual spreadsheet entry

Stats: Mean / SD / CV% auto
06
Data Output & Connectivity

USB and RS-232 output transmits test results to PC or LIMS. Thermal or external printer connection for immediate test certificates. Stored results retrievable for traceability and audit trail requirements

Output: USB / RS-232 / Printer
Industry Applications

Where air permeability testing is specified as a critical quality parameter

Apparel & Sportswear

Breathability is a primary comfort attribute in activewear, base layers, and outdoor clothing. Air permeability testing validates thermal comfort claims, guides fabric selection for activity-specific garments, and supports functional labelling for end consumers

Protective & Medical Textiles

PPE fabrics, surgical gowns, drapes, and isolation apparel must balance barrier protection against air permeability for wearer comfort during extended use. Testing confirms compliance with EN 13795 and ANSI/AAMI PB70 barrier classification requirements

Industrial Filtration Media

Air and liquid filtration fabrics must achieve precise permeability to balance filtration efficiency against pressure drop. Tighter fabrics capture smaller particles but increase system energy demand — permeability testing at multiple pressures characterises this trade-off

Geotextiles & Civil Engineering

Geotextile fabrics used in drainage, separation, and filtration applications must allow water and air flow while retaining soil particles. Air permeability correlates with water permeability and pore size — used as a rapid QC proxy for hydraulic conductivity in field-deployed materials

Automotive Textiles

Automotive seat fabrics, headliners, carpet backing, and acoustic insulation materials are specified for air permeability to control cabin ventilation, seating comfort, and sound absorption performance in vehicle interior systems

Healthcare & Wound Care

Wound dressings and advanced wound care membranes require controlled permeability — sufficient for moisture vapour transmission and oxygen exchange while preventing bacterial ingress. Air permeability is part of the characterisation panel for CE-marked wound care devices

Test Standards & Pressure Comparison

How major international air permeability standards differ in test conditions and reporting

ISO 9237 — Textiles
Test pressure: 100 Pa | Test area: 20 cm² (standard) | Units: mm/s | Scope: Woven, knitted, nonwoven fabrics. Most widely used international standard for apparel and technical textiles
ASTM D737 — Standard Air Permeance
Test pressure: 125 Pa | Test area: 38 cm² | Units: cfm/ft² | Scope: Textile fabrics. Dominant US standard — results not directly comparable to ISO 9237 due to different pressure and area
EN ISO 9073-15 — Nonwovens
Test pressure: 200 Pa | Scope: Nonwoven fabrics specifically. Higher test pressure reflects the tighter pore structure typical of nonwoven filtration and barrier materials
ISO 11058 — Geotextiles
Test pressure: 200 Pa | Units: m³/m²/s | Scope: Geotextiles and geosynthetics. Larger test area specified to account for the high variability in open geotextile structures
Pressure vs Application Matrix
50 Pa — Very Open Structures
Coarse geotextiles, open weave shade nets, horticultural meshes. Low pressure prevents turbulent flow artefacts in large-pore fabrics
100 Pa — Standard Apparel & Technical
ISO 9237 standard condition. Woven apparel, sportswear, workwear, nonwovens, laminates. Reference condition for most textile product standards
125–200 Pa — Filtration & Protective
ASTM D737, EN ISO 9073-15. Filter media, PPE fabrics, medical barriers, automotive felts. Higher pressure better simulates operating differential in use
500 Pa — Dense Filter Media
High-efficiency filter cartridges, HEPA pre-filter layers, speciality barrier membranes. High test pressure discriminates between very similar low-permeability structures
Cross-Standard Comparisons: Results from different test pressures and test areas cannot be directly compared. When reporting or specifying air permeability, always state the test standard, test pressure, and test area alongside the numeric result to enable valid comparison between laboratories and supplier certifications.
Air Permeability in the Fabric QC Workflow

Where testing integrates within the textile quality assurance pipeline

Incoming Fabric Receipt
Fabric roll received from supplier with mill certificate. Permeability spec stated on purchase order

Conditioning
20°C / 65% RH for 24h per ISO 139 — moisture content affects permeability; conditioning ensures comparable results

Permeability Test
Fison Tester — 10 readings across width; mean, SD, CV% calculated automatically

Specification Check
Result compared to min/max specification. Pass → release. Fail → hold for disposition review

LIMS / Report
Data exported via USB/RS-232 to LIMS. Test certificate generated for batch traceability record
Statistical Note: ISO 9237 recommends a minimum of 10 test readings per specimen lot, taken across the full fabric width. CV% above 10% indicates significant within-roll variation and may signal weaving or finishing process instability requiring supplier corrective action.
Technical Specifications
ParameterSpecificationStandard / Compliance
Measurement Range0 – 5000 mm/s (0 – 500 cm³/cm²/s)ISO 9237
Measurement Accuracy±2% of readingISO 9237
Test Pressure Range20 – 500 Pa (selectable)ASTM D737
Test Area Options1 / 5 / 10 / 20 cm²EN ISO 9073-15
Display Unitsmm/s, cm³/cm²/s, L/m²/s, cfm/ft²ISO 9237
Pressure SensorDigital transducer, ±0.5 Pa resolutionIEC 61010-1
Flow SensorCalibrated mass flow, traceable to NPL/NISTISO 17025
Statistics OutputMean, SD, Min, Max, CV% (up to 10 readings)ISO 2859-1
Conditioning Requirement20°C ±2°C / 65% ±4% RH per ISO 139ISO 139
Data OutputUSB, RS-232, printer portISO 11058
Power Supply220–240V / 50–60 HzIEC 62133
CertificationCE marked, RoHS compliantEN 60204-1
Frequently Asked Questions

Air permeability is governed by fabric pore structure — determined by fiber type and diameter, yarn count, twist level, weave or knit construction, thread density (threads per cm), and finishing treatments. Coarser yarns and lower thread counts create larger inter-yarn gaps, increasing permeability. Higher twist yarns are more compact, reducing permeability. Finishing treatments such as calendaring (hot pressing), coating, laminating, or resin finishing block pores and dramatically reduce permeability. Moisture content also affects permeability — hygroscopic fibers swell when wet, reducing pore dimensions, which is why conditioning at standard atmosphere (20°C/65% RH) before testing is mandatory for reproducible results.

ISO 9237 applies 100 Pa test pressure across a 20 cm² test area and reports in mm/s. ASTM D737 applies 125 Pa across a 38 cm² area and reports in cfm/ft². Since air permeability is pressure-dependent (higher pressure drives more airflow through the same fabric), results at 100 Pa and 125 Pa cannot be directly equated — the relationship is non-linear and fabric-specific. The different test areas also affect results when fabric has structured permeability variation (like woven fabrics where open area fraction varies with weave geometry). To compare results across standards, always report the test standard, pressure, and area together with the measured value.

ISO 9237 recommends a minimum of 10 specimens per fabric lot, taken at different positions across the full width of the roll — avoiding selvages (within 10 cm of fabric edge). This sampling pattern captures the across-width variation introduced by loom tension gradients, finishing machine edge effects, and calendering pressure variability. CV% above 10% indicates significant within-roll variation that warrants investigation. For incoming inspection under AQL sampling plans, the number of rolls sampled per consignment is governed by lot size under ISO 2859-1 — with one specimen strip cut from each selected roll for permeability testing.

Air permeability and moisture vapour transmission rate (MVTR) are related but distinct properties. Air permeability measures bulk airflow through fabric pores under pressure differential — relevant to convective heat and mass transfer. MVTR measures the rate of water vapour diffusion through the fabric under a concentration gradient — relevant to evaporative cooling (sweat evaporation). In open fabrics, both properties are high. In microporous membranes (e.g. PTFE laminates), MVTR can be high while air permeability is near zero — the membrane passes water vapour by diffusion through pores too small for bulk air flow. Both are measured independently in performance textile characterisation, and specifications for breathable outerwear typically include both parameters.

Calibration follows a two-part protocol. Flow calibration: verify instrument reading against a certified reference orifice plate or calibrated flow standard — typically performed annually or after any repair to the flow circuit. Pressure calibration: verify the differential pressure transducer reading against a traceable pressure reference — check that the instrument achieves stable target pressure (e.g. 100 Pa ±2 Pa) during a test run. Daily maintenance includes checking gasket integrity on test heads (replace if cracked or compressed), verifying flow path is clean and free from fibre debris, and confirming calibration reference using a fabric reference standard of known permeability. All calibration records should be traceable to national standards per ISO 17025 requirements.

Test area selection depends on fabric structure: 1 cm² heads are used for very coarse open weaves or leno fabrics where a larger head would span fewer than 10 complete repeat units — distorting the result. Standard 20 cm² heads are specified by ISO 9237 for most woven and knitted apparel fabrics where the repeat unit is small relative to the test area. Nonwoven fabrics typically use 20 cm² under EN ISO 9073-15. Geotextiles under ISO 11058 use larger areas to account for the high spatial variability of open drainage fabrics. The guiding principle is that the test area should encompass at least 10 complete weave or structure repeats — ensuring the measured airflow represents the average open area of the fabric rather than a single pore.

Add Precision Air Permeability Testing to Your Fabric QC Programmer

Explore the Fison Air Permeability Tester — built for ISO 9237 and ASTM D737 compliance, designed for textile laboratories requiring accurate, repeatable fabric airflow measurement.

View ProductContact Fison