How to Measure the Permeability of a Plastic Film

Measuring the permeability of a plastic film helps manufacturers, material developers and laboratories understand how gases and water vapor pass through a material. These measurements are important when comparing film formulations, evaluating barrier properties and selecting materials for packaging applications.

The appropriate test depends on the substance being measured, the film characteristics and the intended application. Oxygen transmission rate (OTR), water vapor transmission rate (WVTR) and carbon dioxide transmission rate (CO₂TR) are commonly used to characterize different aspects of film barrier performance.

This guide explains how plastic film permeability is evaluated, which conditions influence the results and what to consider when choosing a measurement system.

1. Define the Property You Need to Measure

Before starting a test, identify which substance needs to be measured and what information the result should provide.

Oxygen Transmission Rate (OTR)

OTR measures the rate at which oxygen passes through a film under specified test conditions. It is relevant when evaluating materials intended to limit oxygen transmission.

Learn more in [Oxygen Permeability and OTR: Measurement and Analysis].

Water Vapor Transmission Rate (WVTR)

WVTR measures the rate at which water vapor passes through a film under specified conditions. It is particularly relevant when evaluating moisture barrier properties.

Learn more in [Water Vapor Permeability and WVTR: Measurement and Analysis].

Carbon Dioxide Transmission Rate (CO₂TR)

CO₂TR measures the rate at which carbon dioxide passes through a film under specified conditions. It can be useful when carbon dioxide exchange is relevant to the intended application.

Learn more in [CO₂ Permeability and CO₂TR: Measurement and Analysis].

These parameters are not interchangeable. A film’s performance against one substance does not automatically indicate its performance against another.

2. Select a Suitable Test Method

The measurement method must be appropriate for the material, the substance being measured and the expected transmission values.

In many film testing systems, a sample is mounted between two chambers. One side is exposed to the gas or vapor of interest, while the other side is used to detect or measure the substance that passes through the sample.

The instrument records the transmission behavior over time and uses the measurement data to determine the relevant transmission parameter.

The specific apparatus, detection principle and calculation procedure depend on the selected method and instrument. The test should therefore be planned according to the applicable method rather than assuming that every system uses the same procedure.

3. Prepare the Plastic Film Sample

Sample preparation is an important part of permeability testing. An unsuitable sample or an incorrect mounting procedure can affect the measurement and make comparisons less reliable.

Before testing, consider the following points:

• Sample condition: ensure that the film is representative of the material being evaluated.
• Thickness: measure or document thickness where required by the test method.
• Surface condition: inspect the sample for folds, wrinkles, scratches or other visible defects.
• Sample dimensions: prepare a sample that fits the instrument’s test area and mounting requirements.
• Mounting and sealing: follow the instrument instructions to prevent unintended leakage around the sample.
• Conditioning: apply any conditioning procedure required by the selected method.

For multilayer films and laminates, the sample should represent the complete structure when the objective is to evaluate the barrier performance of the finished material.

Learn more about Permeability Testing of Multilayer Films and Laminates.

4. Define the Test Conditions

Permeability measurements are influenced by the conditions under which the test is performed. These conditions must be defined and documented to support meaningful comparisons.

Temperature

Temperature can influence the rate at which a substance passes through a material. Tests intended for comparison should use consistent, specified temperature conditions.

Relative Humidity

Humidity can affect the behavior of some materials, particularly moisture-sensitive polymers and barrier layers. This is especially relevant when measuring water vapor transmission or testing materials whose properties change with moisture exposure.

Gas and Pressure Conditions

For gas transmission measurements, the gas being tested and the driving force across the sample are important factors. The selected test method defines how these conditions should be established and controlled.

Measurement Range

The expected transmission value should fall within the suitable measurement range of the instrument and method. If the material’s performance is unknown, preliminary information or exploratory testing may help determine an appropriate setup.

Test Duration and Stability

The measurement must follow the method’s requirements for establishing and evaluating transmission behavior. The time needed to obtain a usable result can depend on the material, the parameter and the test system.

Documenting the conditions is essential when comparing materials, reviewing historical results or investigating changes in performance.

5. Perform the Measurement

Although the exact procedure varies by instrument, a typical film permeability test follows a sequence of defined steps.

1. Check the instrument: confirm that the system is suitable for the material and the required transmission parameter.
2. Prepare the sample: inspect, prepare and condition the film as required.
3. Mount the sample: place it in the test area and follow the specified sealing procedure.
4. Set the test conditions: establish the required temperature, humidity and gas conditions.
5. Run the test: operate the instrument according to the selected method.
6. Review the data: check that the measurement meets the method’s requirements and that the result is usable.
7. Record the result: document the measured parameter, units, sample information and test conditions.

This sequence is a general overview, not a substitute for the operating instructions or the requirements of a specific test method.

6. Understand the Results

Once the test is complete, it is important to understand what the reported value represents.

Transmission Rate

A transmission rate describes the amount of a substance passing through a specified area of material over a given period under defined conditions.

For example, OTR expresses oxygen transmission, while WVTR expresses water vapor transmission. The units and reporting conventions depend on the method and instrument.

Permeability Coefficient

A permeability coefficient describes a material’s permeability while accounting for the driving force for transport and, in common approaches, the material thickness.

A transmission rate and a permeability coefficient are different quantities. They should not be compared directly without considering the calculation method, units and relevant conditions.

Comparing Different Films

When comparing film samples, check that the results refer to comparable:

• Test parameters and units.
• Temperature and relative humidity conditions.
• Gas or vapor conditions.
• Sample thickness and structure.
• Test methods and reporting conventions.

A lower transmission rate generally indicates less transmission under the stated conditions, but the practical significance depends on the parameter, the material and the intended application.

7. What Can Affect the Accuracy and Repeatability of a Test?

Several factors may influence the reliability of a permeability measurement.

Sample leakage: inadequate sealing can allow gas to bypass the film and distort the result.

Sample damage: punctures, folds or other defects can affect the measured behavior and may not represent the intended material.

Inconsistent conditioning: differences in sample history or conditioning can make results more difficult to compare.

Changing test conditions: differences in temperature, humidity or other controlled variables can affect transmission behavior.

Incorrect sample identification: confusing film structures, thicknesses or sample orientations can lead to misleading comparisons.

Unsuitable measurement range: an instrument or method that is not appropriate for the expected transmission values may not provide the required information.

Following the selected test method, checking the sample mounting and documenting test conditions help support repeatable measurements.

8. How to Choose a Permeability Tester for Plastic Films

The most suitable instrument depends on the film materials, the parameters to be measured and the laboratory’s requirements.

When evaluating a system, consider:

• Measurement parameters: OTR, WVTR, CO₂TR or multiple parameters.
• Material compatibility: the film composition, thickness and structure.
• Measurement range: the expected transmission values.
• Environmental control: the required temperature and relative humidity.
• Test methods: the procedures and reporting requirements relevant to your application.
• Laboratory workflow: sample throughput, data handling and reporting.
• Future requirements: whether additional transmission parameters may need to be evaluated.
• For laboratories testing several types of barrier materials, a system capable of measuring more than one parameter may help consolidate testing activities. The instrument’s suitability should be confirmed against the actual samples and methods.

9. ExtraSolution Solutions for Film Permeability Testing

ExtraSolution offers solutions for measuring oxygen, carbon dioxide and water vapor transmission through films and barrier materials. The appropriate instrument depends on the measurement parameters and the intended application.

MultiPerm O2-CO2

Designed for oxygen transmission rate (OTR) and carbon dioxide transmission rate (CO₂TR) measurements.

Explore MultiPerm O2-CO2.

MultiPerm O2-H2O

Designed for oxygen transmission rate (OTR) and water vapor transmission rate (WVTR) measurements.

Explore MultiPerm O2-H2O.

MultiPerm H2O-CO2

Designed for water vapor transmission rate (WVTR) and carbon dioxide transmission rate (CO₂TR) measurements.

Explore MultiPerm H2O-CO2.

TotalPerm

Combines OTR, CO₂TR and WVTR measurement capabilities in one integrated system.

Explore TotalPerm.

PermeH2O

Provides a dedicated solution for water vapor transmission rate (WVTR) measurement.

Explore PermeH2O.

Instrument suitability depends on the material, expected transmission values, test method and required configuration. Contact ExtraSolution to discuss your samples and identify a suitable testing solution.

Conclusion

Measuring the permeability of a plastic film requires a clearly defined test objective, an appropriate method, careful sample preparation and controlled test conditions.

OTR, WVTR and CO₂TR provide different information about film barrier performance. Understanding which parameter is relevant, how the result is reported and which conditions affect the measurement helps laboratories compare materials and make better-informed decisions.

ExtraSolution provides solutions for measuring oxygen, carbon dioxide and water vapor transmission through films and barrier materials.

Contact ExtraSolution to discuss your film testing requirements and identify a suitable measurement system.