Synthetic Leather Breathability Testing: Standards, Methods and Technical Requirements

Synthetic leather breathability testing measures the water vapor transmission and air permeability performance of PU, PVC, and microfiber synthetic leather materials, which directly determines wearing comfort, hygiene, and product grade. This article provides a comprehensive technical overview of sample types, testing items, standard test methods such as ASTM E96, ISO 2528, ISO 9237, and their applications across footwear, apparel, automotive, and furniture industries. Accredited third-party laboratories rely on these standardized procedures to deliver reproducible, comparable breathability data for quality control and product development.

Technical Overview

Synthetic leather, including polyurethane (PU), polyvinyl chloride (PVC), semi-PU, and microfiber-based materials, has become a major substitute for natural leather in footwear, apparel, upholstery, automotive interiors, and consumer goods. Because the polymer coating layer forms a relatively continuous film, synthetic leather is inherently less permeable than natural hide, and breathability therefore becomes one of the most critical comfort and quality performance indicators. Breathability testing quantifies the ability of the material to transmit water vapor generated by human perspiration and, in some cases, to allow air flow through the structure.

Two principal properties are evaluated in synthetic leather breathability testing: water vapor permeability, expressed as the water vapor transmission rate (WVTR) in grams per square meter per 24 hours (g/m²·24h), and air permeability, expressed as the air flow velocity through the specimen under a defined pressure difference, typically in mm/s. These measurements support material grading, comparison with genuine leather, validation of microporous coating technology, verification of micro-perforation processes, and assessment of fitness for purpose in end-use applications such as shoe uppers, linings, garments, and seating surfaces.

Breathability testing is typically performed by accredited third-party laboratories using gravimetric dish methods, dynamic air permeability instruments, and specialized footwear comfort test protocols. Testing must be conducted under strictly controlled temperature, humidity, and airflow conditions, because the permeation of water vapor through polymer layers is highly sensitive to the humidity gradient across the specimen.

Testing Samples

PU Synthetic Leather

Both dry-process and wet-process polyurethane synthetic leather can be tested. Wet-process PU, which contains a microporous coagulated layer, generally shows substantially higher water vapor transmission than dry-process PU. Specimens should be representative of full production width and taken away from edges and seams. Samples with surface finishes, embossing, or top coats should be tested in their final finished state, since finishing operations can significantly reduce permeability.

PVC Synthetic Leather

Polyvinyl chloride synthetic leather usually exhibits low water vapor permeability because of its dense plasticized film structure. Testing is important for verifying whether foaming layers, plasticizer content, or perforation treatments have achieved the required breathability level for applications such as furniture upholstery and automotive trim.

Microfiber Synthetic Leather

Microfiber synthetic leather, constructed from ultrafine fiber bundles impregnated with polyurethane, is engineered to approach the hand feel and permeability of genuine leather. Breathability testing is used to benchmark microfiber materials against natural leather reference values and to qualify them for premium footwear and apparel applications.

Semi-PU and Coated Fabrics

Semi-PU materials with a PU surface layer on a PVC or fabric substrate, as well as breathable coated fabrics with hydrophilic or microporous membranes, are tested to confirm moisture management performance after lamination and finishing.

Finished Components and Processed Panels

Laminated assemblies, perforated panels, sprayed or finished cuttings, and complete footwear upper assemblies can be evaluated to measure how processing steps such as adhesive lamination, embossing, and surface coating affect the final breathability of the product.

Testing Items

• Water vapor permeability (WVTR), expressed in g/m²·24h, determined under controlled temperature and humidity gradients.
• Water vapor absorption and desorption, relevant for footwear lining and insole materials under EN ISO 20344 based protocols.
• Air permeability, expressed as flow rate in mm/s at a specified pressure differential, typically 100 Pa or 200 Pa.
• Breathability retention after physical treatments, including repeated flexing, abrasion, and accelerated aging.
• Comparative permeability evaluation between synthetic leather and natural leather reference materials.
• Verification of the effectiveness of microporous structures, hydrophilic coatings, and micro-perforation patterns.

Testing Methods

Gravimetric Dish Method for Water Vapor Transmission

The most widely used approach follows ASTM E96, ISO 2528, and GB/T 12704, in which the specimen is sealed over a dish containing either distilled water or a desiccant. The assembly is placed in a controlled atmosphere, commonly at 38°C with 90% relative humidity or at 23°C with 50% relative humidity depending on the selected procedure. In the water method, vapor passes from inside the dish through the specimen to the drier environment; in the desiccant method, vapor is driven from the humid environment into the dish. The dish is weighed periodically, and the water vapor transmission rate is calculated from the mass change per unit time and unit test area. An inverted cup variant may be used for materials expected to show high transmission or when direct water contact with the surface is relevant to end use.

Leather-Specific Permeability Method

ISO 14268 and the corresponding GB/T 4689 series describe the determination of water vapor permeability specifically for leather and leather-like sheet materials. The specimen is clamped over a rotating or stationary vessel containing a desiccant or water, and the mass change is recorded under a defined rotary speed and ambient condition. This method is commonly selected when synthetic leather is intended to replace natural leather and must be compared on an equivalent basis.

Air Permeability Method

Air permeability is determined in accordance with ASTM D737, ISO 9237, or GB/T 5453. A specimen is clamped in a circular test head, and a controlled pressure differential is applied across the material face. The rate of air flow through the specimen is measured and expressed as the volume of air per unit area per unit time or as flow velocity in mm/s. Fully coated synthetic leather without perforation typically exhibits an air permeability close to zero, so this test is most informative for perforated, microporous, or textile-backed structures.

Footwear Comfort Protocols

For safety footwear and occupational footwear, EN ISO 20344 defines water vapor permeability and water vapor absorption and desorption requirements for upper and lining materials. The permeability test uses a capsule system, while absorption and desorption are determined from the mass change of a specimen in contact with a wetted surface over defined time intervals. These results demonstrate whether footwear uppers can dissipate perspiration during wear.

Sweating Guarded-Hotplate Method

For garment and comfort-oriented applications, ISO 11092 may be applied to determine the water vapor resistance (Ret) of synthetic leather laminates and assemblies. The specimen is placed on a porous heated plate that simulates sweating skin, and the steady-state evaporative heat flux is measured. Lower Ret values indicate better moisture transfer and improved physiological comfort.

Test Condition Control and Key Influencing Factors

All specimens must be conditioned before testing in a standard atmosphere appropriate to the applicable standard, for example 23°C with 50% relative humidity for leather-type materials. Critical factors affecting accuracy include the integrity of the edge seal around the dish, the stability of the temperature and humidity gradient, air velocity across the specimen surface, specimen thickness and coating structure, and the direction of the humidity gradient. Replicate specimens are normally tested, and results are reported with the test method, condition set, and units clearly identified.

Applications

• Footwear manufacturing: qualification of shoe upper, lining, and insole materials for breathability and perspiration management, including compliance support for safety footwear standards.
• Apparel and accessories: evaluation of garments, gloves, bags, and watch straps where skin contact comfort and moisture dissipation are required.
• Automotive interiors: assessment of seat and door trim materials for thermal comfort and reduced condensation in vehicle cabins.
• Furniture upholstery: verification that coated upholstery materials maintain acceptable moisture behavior for long-term seating comfort and hygiene.
• Sports goods: qualification of ball coverings, protective gear, and athletic equipment covers for moisture handling.
• Research and development: optimization of microporous PU formulations, hydrophilic coatings, perforation patterns, adhesive systems, and finishing processes.
• Quality control and supplier verification: incoming material inspection, batch consistency monitoring, and benchmarking against genuine leather performance levels.

FAQ

What is breathability in synthetic leather?

Breathability refers to the capacity of the material to allow water vapor produced by the human body to pass through its structure. It is quantified mainly as the water vapor transmission rate in g/m²·24h and, where relevant, as air permeability in mm/s.

What is the difference between water vapor permeability and air permeability?

Water vapor permeability measures the diffusion of moisture molecules through or along the polymer structure under a humidity gradient, while air permeability measures convective air flow through open pores or perforations under a pressure difference. A material can have measurable vapor transmission while remaining essentially airtight.

What breathability values are typically expected?

Performance varies widely with structure and thickness. Conventional dry-process PU and PVC materials may show WVTR values below several hundred g/m²·24h, whereas well-engineered wet-process PU and microporous microfiber materials can reach values of several thousand g/m²·24h, approaching the comfort performance of natural leather. Specific acceptance limits should be agreed between buyer and supplier based on the end use.

Which standard should be selected for testing?

The choice depends on the product and market. ASTM E96, ISO 2528, and GB/T 12704 are general gravimetric methods for sheet materials; ISO 14268 and the GB/T 4689 series are leather-oriented; ASTM D737, ISO 9237, and GB/T 5453 cover air permeability; and EN ISO 20344 applies to footwear applications. Accredited third-party laboratories can advise on the most appropriate method and condition set.

How can the breathability of synthetic leather be improved?

Common approaches include using wet-process microporous PU structures, applying hydrophilic polyurethane coatings, reducing the thickness of surface finishes, introducing micro-perforation, selecting breathable adhesives and substrates, and optimizing foaming and coagulation processes during production.

What sample preparation is required?

Specimens must be clean, flat, and free of wrinkles and damage, taken from representative production material, and conditioned in a standard atmosphere before testing. The number of specimens and dimensions are specified by the applicable test method, and replicates are recommended to account for material variability.