Plastic Film and Sheeting Air Permeability Testing: Standards, Methods, and Applications

Air permeability testing of plastic film and sheeting measures the rate at which gases pass through polymeric materials under controlled conditions of pressure, temperature, and humidity. This testing is essential for validating barrier performance in food packaging, agricultural films, construction membranes, and medical applications. This article explains the key testing standards, sample types, methods, and practical considerations for plastic sheet permeability evaluation.

Technical Overview

Air permeability testing, also referred to as gas permeability or gas transmission testing, quantifies how readily air and other gases pass through plastic films and sheeting. Because polymer chains are not perfectly dense, gas molecules can dissolve into the material on the high-pressure side, diffuse through the polymer matrix, and desorb on the low-pressure side. This solution-diffusion mechanism determines the barrier properties of the material.

For plastic sheeting, permeability performance is typically expressed as the gas transmission rate (GTR), oxygen transmission rate (OTR), water vapor transmission rate (WVTR), or air permeance. These values directly influence product shelf life, moisture protection, breathing performance, and regulatory compliance. Accredited third-party laboratories perform these tests using instrumented methods defined by international standards organizations such as ISO, ASTM, and the Chinese national standards body (GB).

Key parameters that influence test results include material thickness, crystallinity, additives, temperature, and relative humidity. For this reason, all recognized test methods require strict conditioning of specimens and control of the test environment.

Testing Samples

Single-Layer Polyolefin Films

Low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), and polypropylene (PP) films are the most commonly tested materials. These films are used in food packaging bags, agricultural mulch films, and protective covers. Typical thickness ranges from 10 µm to 200 µm, and specimens must be flat, free of pinholes, creases, and contamination.

PVC Sheeting and Coated Tarpaulins

Polyvinyl chloride sheeting, including laminated and coated fabrics used for truck covers, tents, and waterproof membranes, is tested to evaluate both gas barrier performance and controlled breathability. Reinforced or fabric-backed samples require special specimen preparation to ensure a leak-free seal in the test cell.

Multilayer and Composite Structures

Coextruded and laminated structures, such as PE/EVOH/PE or PET/AL/PE constructions, are tested as complete systems because the overall permeability depends on the combined resistance of every layer. Testing is performed on the finished laminate rather than on individual components.

Breathable and Microporous Films

Microporous films, hydrophilic films, and breathable membranes used in hygiene products, medical gowns, and building wraps are tested for water vapor transmission and air flow to confirm their controlled permeability characteristics.

Sample Preparation Requirements

• Specimens must be representative of the production batch and free from defects.
• Conditioning is typically performed at 23 °C ± 2 °C and 50% ± 5% relative humidity for a minimum of 24 hours unless otherwise specified.
• A minimum of three specimens per material is recommended to account for variability.
• Specimen diameter and sealing method must match the requirements of the selected test instrument.

Testing Items

Depending on the intended application, the following permeability parameters can be evaluated for plastic films and sheeting:

• Gas transmission rate (GTR): The general volume of gas passing through a unit area of the specimen per unit time, expressed in cm³/(m²·24h·0.1 MPa).
• Oxygen transmission rate (OTR): Critical for food packaging, pharmaceutical packaging, and any application where oxidation must be limited.
• Water vapor transmission rate (WVTR): Expressed in g/(m²·24h); important for moisture-sensitive products, construction membranes, and breathable films.
• Carbon dioxide transmission rate (CO2TR): Relevant for modified atmosphere packaging (MAP) of fresh produce, where CO2 loss and O2 ingress must be balanced.
• Nitrogen and other gas permeability: Used for specialty packaging, inflatables, and industrial barrier applications.
• Air permeance (airflow-based): Applied to porous or textile-like sheeting where air passes through open pores rather than through the polymer matrix, expressed in units such as cm³/(cm²·s) or L/(m²·s).
• Permeability coefficient (P) and diffusion coefficient (D): Fundamental material constants derived from transmission measurements for research and material comparison purposes.

Testing Methods

Differential-Pressure Method (Manometric / Volumetric)

The specimen is mounted as a sealed barrier between two chambers. One side is evacuated or pressurized with the test gas while the other side is maintained at low pressure. The increase in pressure (or volume) on the low-pressure side is measured over time and converted into a gas transmission rate. This method is versatile because it can be used with any pure test gas.

• ASTM D1434 — Standard Test Method for Determining Gas Permeability Characteristics of Plastic Film and Sheeting.
• ISO 2556 — Determination of the gas transmission rate of films and thin sheets under atmospheric pressure (manometric method).
• ISO 15105-1 — Film and sheeting: determination of gas-transmission rate, differential-pressure method.
• GB/T 1038 — Determination of gas transmittance of plastic films and sheeting by the differential-pressure method.

Equal-Pressure Method (Coulometric Sensor)

The specimen separates two chambers maintained at equal total pressure. A carrier gas (typically nitrogen) flows on one side, while the test gas (oxygen) flows on the other. Oxygen that permeates through the specimen is carried to a coulometric sensor, which quantifies the transmission rate with high sensitivity, making it suitable for high-barrier materials.

• ASTM D3985 — Standard Test Method for Oxygen Gas Transmission Rate Through Plastic Film and Sheeting Using a Coulometric Sensor.
• ISO 15105-2 — Film and sheeting: determination of gas-transmission rate, equal-pressure method.
• GB/T 19789 — Determination of oxygen transmittance of packaging materials by the coulometric sensor method.

Water Vapor Transmission Methods

WVTR is determined either gravimetrically, by monitoring the weight change of a dish containing desiccant covered by the specimen, or instrumentally, using infrared sensors that detect moisture permeating through the specimen. Standard conditions typically include 38 °C and 90% relative humidity for high-barrier materials.

• ASTM E96 / ASTM F1249 — Water vapor transmission of materials (gravimetric dish method / modulated infrared sensor method).
• ISO 15106 — Plastics: film and sheeting, determination of water vapour transmission rate.
• GB/T 1037 / GB/T 21529 — Water vapor transmission rate by the cup method and by the infrared sensor method.

Airflow-Based Permeance Methods for Porous Sheeting

For microporous, woven, or coated fabrics where permeation occurs through physical pores, air permeance is measured by forcing a controlled airflow through the specimen under a fixed pressure differential. This approach is common for tarpaulins, building wraps, and technical textiles.

• ASTM D737 — Standard Test Method for Air Permeability of Textile Fabrics.
• ISO 5636 — Paper and board: determination of air permeance (Bendtsen, Gurley, and Sheffield methods), applicable to certain sheet substrates.
• GB/T 5453 — Determination of permeability of fabrics to air.

Method Selection Considerations

• Use the differential-pressure method for multi-gas flexibility and fundamental material characterization.
• Use the coulometric equal-pressure method for high-barrier oxygen-sensitive structures and packaging validation.
• Use airflow permeance methods for porous sheeting where visible porosity dominates gas transport.
• Test at conditions that reflect real-world service, including elevated temperature or humidity when applicable.

Applications

Air permeability test results for plastic sheeting support a wide range of industries and use cases:

• Food packaging: Selecting films with defined OTR and CO2TR for modified atmosphere packaging of fresh produce, meat, and snacks, extending shelf life while preserving freshness.
• Agriculture: Verifying greenhouse films and mulch films that balance heat retention with controlled gas exchange to promote crop growth.
• Construction: Qualifying vapor barriers, roofing underlayments, and breathable building membranes that manage moisture migration while maintaining structural durability.
• Medical and pharmaceutical: Validating sterile barrier systems and breathable medical films where controlled permeation supports sterility and comfort.
• Hygiene and apparel: Confirming that microporous films used in diapers and protective clothing achieve the required breathability for user comfort.
• Industrial and logistics: Evaluating tarpaulins, protective covers, and industrial packaging liners for weather resistance and controlled air exchange.
• Quality control and R&D: Comparing resin grades, coatings, and processing parameters; supporting incoming material inspection, lot release testing, and failure analysis.

FAQ

What is the difference between air permeability and gas transmission rate?

Air permeability usually refers to bulk airflow through open pores in porous or textile-like sheeting, measured as air permeance under a pressure differential. Gas transmission rate refers to permeation through a nominally dense polymer film via the solution-diffusion mechanism and is expressed as gas volume per unit area per unit time.

Which test standard should I choose?

The choice depends on the material, application, and target market. ASTM D1434 or ISO 15105-1 (differential pressure) suit general-purpose characterization; ASTM D3985 or ISO 15105-2 (coulometric) suit oxygen barrier validation; ASTM D737 or GB/T 5453 suit porous fabrics. Accredited third-party laboratories can advise on the most appropriate method for regulatory or customer requirements.

How do temperature and humidity affect results?

Permeability increases significantly with temperature, and for hydrophilic polymers such as EVOH and certain polyamides, humidity can raise oxygen transmission rates by orders of magnitude. For this reason, standard test conditions must always be reported alongside results.

What do the reported units mean?

A typical oxygen transmission result in cm³/(m²·24h·0.1 MPa) means the volume of oxygen, in cubic centimeters, that permeates one square meter of material over 24 hours under a standard pressure differential. Water vapor results in g/(m²·24h) express the mass of moisture transmitted per square meter per day.

How many specimens are needed for a reliable result?

Most standards require a minimum of three specimens per sample, with the mean value reported. For heterogeneous materials such as coated fabrics, additional specimens improve the statistical reliability of the result.

Can coated or printed films be tested?

Yes. Coatings, inks, and surface treatments are integral parts of the finished structure, and testing is performed on the complete material to reflect actual product performance.

How long does a typical test take?

High-barrier materials may require 24 to 48 hours or longer to reach equilibrium before steady-state transmission values can be recorded, while permeable porous sheeting can often be measured within minutes. Laboratories typically report results within several business days depending on conditioning and equilibrium requirements.