Air permeability testing of leather for clothing measures how readily air passes through garment leather under a controlled pressure differential, providing a quantitative index of breathability, wearing comfort and finishing quality. This technical article explains the test principle, applicable international and national standards such as ISO 9237, ASTM D737, ISO 14268 and QB/T 2799, typical sample types, test procedures, data interpretation and practical applications. It is written for leather manufacturers, garment brands, quality engineers and sourcing teams who need reliable breathability data from accredited third-party laboratories.
Technical Overview
Air permeability is the property of a material that allows air to flow through its structure when a pressure difference exists across its two surfaces. For clothing leather, it is defined as the volume of air passing through a unit area of the leather per unit time under a specified pressure differential, and it is typically expressed in units such as mm/s or cm³/(cm²·s). Because leather is a natural collagen fiber network penetrated by hair follicle channels and pores, its breathability is a direct reflection of both the raw hide structure and the processing route used in tanning, retanning, fatliquoring, drying and finishing.
High air permeability in garment leather contributes to thermal comfort, effective dissipation of body heat and moisture, and a pleasant, non-clammy hand feel during wear. Conversely, very low permeability often indicates heavy polymer coating, tight lamination, or excessive compaction of the fiber structure, which can compromise comfort and hygiene performance. For these reasons, air permeability is widely specified by garment brands as a routine quality control parameter, alongside the complementary property of water vapour permeability, and testing is commonly performed by accredited third-party laboratories using calibrated permeability instruments.
- Raw material factors: hide or skin origin, follicle density, corium thickness and fat content
- Processing factors: tannage type, degree of retanning, fatliquoring level, drying method and thickness reduction
- Finishing factors: base coat and top coat loading, pigment coverage, embossing and plating intensity
- Construction factors: lamination with textile or foam layers, bonding and flocked backings
Testing Samples
Samples should be taken from representative, production-grade material that is free from visible defects such as scratches, cracks, loose grain or uneven coating. Specimens are die-cut from positions agreed between the parties, avoiding the belly and flank edge zones unless specifically required, and are conditioned to equilibrium before testing in accordance with ISO 2419.
Sheepskin and Lambskin Garment Leather
Soft, lightweight nappa-style leathers used for premium jackets, coats and fashion garments. Their naturally open and thin structure usually gives the highest air permeability values among garment leathers, making them a benchmark material for comfort-oriented specifications.
Cowhide and Goatskin Garment Leather
Medium to heavyweight leathers used for motorcycle apparel, workwear-style jackets, trousers and vests. Their denser fiber network and thicker cross-section generally yield lower permeability, and the test is used to verify that comfort targets are still achieved after finishing.
Suede, Nubuck and Brushed Finishes
Leathers with buffed surfaces retain an exposed, porous fiber structure and typically show markedly higher air permeability than grain-finished leathers. Testing confirms the openness of the nap and monitors consistency between production batches.
Coated, Laminated and Composite Materials
Heavily pigmented, film-coated, or textile-laminated garment leathers, including double-face and bonded constructions, are tested to quantify how much the coating or adhesive layer suppresses breathability. These materials are the most common source of comfort-related complaints and are therefore a priority category for permeability verification.
Testing Items
The core testing portfolio for clothing leather breathability covers the following items, each linked to an internationally or nationally recognized standard method:
- Air permeability to ISO 9237 / EN ISO 9237 (equivalently GB/T 5453), performed at a pressure differential of 100 Pa for apparel materials, with results reported in mm/s
- Air permeability to ASTM D737, performed at a pressure differential of 125 Pa, with results reported in cm³/s/cm²
- Air permeability of leather to QB/T 2799, the dedicated light-industry method using a volumetric principle for leather materials
- Water vapour permeability to ISO 14268, the cup-based gravimetric method that quantifies true moisture breathability in mg per square centimetre per hour or equivalent units
- Supporting measurements that accompany and contextualize permeability data, including thickness determination to ISO 2589 and standard conditioning to ISO 2419
Testing Methods
Specimen Preparation and Conditioning
Circular or square specimens are cut so that each fully covers the clamping head of the test instrument, with a margin to prevent edge leakage. All specimens are conditioned in a standard atmosphere of 23 ± 2 °C and 50 ± 5 % relative humidity for a minimum of 24 hours, or until mass equilibrium is reached, in accordance with ISO 2419. Depending on the material and the specification, five to ten specimens are prepared so that a statistically meaningful value can be reported.
Pressure Differential Method (ISO 9237 / ASTM D737)
The specimen is clamped over a calibrated test head of known open area, commonly 5, 20, 50 or 100 cm². A fan or pump generates a controlled pressure drop across the specimen, 100 Pa for apparel testing under ISO 9237 or 125 Pa under ASTM D737, and the resulting volumetric flow rate of air through the leather is measured with a flowmeter. Air permeability is calculated as the flow rate divided by the test area, yielding mm/s under ISO 9237 or cm³/s/cm² under ASTM D737. Care is taken to seal the edges and avoid specimen distortion during clamping.
Volumetric Method for Leather (QB/T 2799)
In this dedicated leather method, a circular specimen is mounted in a permeability cell and a fixed pressure differential is maintained across it. The volume of air transmitted through the leather over a measured time interval is determined volumetrically, and the air permeability is expressed as the volume of air passing through unit area of leather per unit time. The method is well suited to genuine garment leathers and is frequently referenced in Chinese market specifications and procurement contracts.
Water Vapour Permeability Test (ISO 14268)
Because perceived breathability in wear is governed by moisture transport as well as air flow, the cup method of ISO 14268 is commonly run in parallel. A specimen is sealed over a cup containing either water or a desiccant, and the assembly is held in a controlled atmosphere with defined air movement over the specimen surface. The cup is weighed before and after the exposure period, and the mass of water vapour transmitted through the leather is converted into a permeability value in mg per square centimetre per hour. This gravimetric result is often the decisive parameter for garment comfort specifications.
Data Evaluation and Reporting
Individual specimen results are evaluated statistically: ISO 9237 calls for reporting the median of the specimen values, while ASTM D737 reports the arithmetic mean. The test report should state the standard used, the pressure differential, the test head area, the number of specimens, the conditioning regime, and the individual and summary results with units. Material direction, if applicable, and any deviation from the standard, such as the use of a smaller test area for high-permeability suedes, must also be documented.
Applications
Air permeability and related breathability data serve multiple purposes across the clothing leather supply chain, from tannery process control to end-product comfort assurance:
- Incoming material inspection and supplier qualification for garment manufacturers and brand sourcing teams
- Batch-to-batch quality control at tanneries, verifying consistency of fatliquoring, milling and finishing operations
- Product development support, comparing candidate finishing formulations, coating loads and lamination constructions for their effect on comfort
- Compliance verification against buyer technical specifications, private-label requirements and comfort-oriented labeling claims
- Failure analysis and complaint investigation, for example diagnosing clamminess or heat stress in finished jackets traced to over-coated leather
- Technical documentation for market access in the European Union, North America and Asia, where breathability limits are increasingly written into apparel performance requirements
FAQ
What is the air permeability of clothing leather?
It is the measured volume of air that passes through a defined area of leather per unit time under a fixed pressure difference, such as 100 Pa under ISO 9237. Higher values indicate a more open, breathable structure; heavily coated or laminated leathers can approach zero permeability, while fine suedes and lightweight lambskins reach substantially higher values.
Why is breathability important for leather garments?
Breathable leather allows body heat and moisture vapor to escape, preventing the hot, sticky microclimate that develops inside non-permeable garments. This directly affects all-day wearing comfort for jackets, coats, trousers and gloves, and low breathability is one of the most common drivers of comfort-related product returns.
Which standard should be selected for testing?
For most apparel applications, ISO 9237 (or its identical national adoption GB/T 5453) at 100 Pa is the default choice. ASTM D737 at 125 Pa is preferred when results must align with North American specifications. QB/T 2799 is used when a dedicated leather-specific method is contractually required, and ISO 14268 is added whenever moisture breathability must be demonstrated in addition to airflow.
How does air permeability differ from water vapour permeability?
Air permeability measures bulk airflow through open pores under a pressure differential, while water vapour permeability measures the diffusion of moisture molecules through the material, including through the polymer phase of coatings. A leather can show low air permeability yet still transmit water vapour, which is why comfort specifications typically address both parameters.
What sample size is required for testing?
Each specimen only needs to cover the clamping head, so swatches of roughly 50 mm × 50 mm per specimen are normally sufficient. In practice, a full laboratory submission of a piece about 30 cm × 30 cm, or a complete garment panel, allows five to ten specimens plus retained material for retesting.
What factors most often reduce leather breathability?
Heavy pigment and top coats, thick film finishes, embossing under high pressure, lamination with adhesive and textile layers, and excessive fatliquoring that clogs the pore structure are the leading causes. Thicker cross-sections and tighter fiber compaction also lower permeability, so tanneries balance these variables against durability and aesthetic requirements.