Oxygen transmission rate (OTR) testing quantifies the amount of oxygen that permeates through plastic films and sheeting under controlled temperature and humidity conditions, making it a critical quality-control parameter for barrier packaging in the food, pharmaceutical, medical device, and electronics industries. This article explains the test principle, applicable international standards such as ASTM D3985 and ISO 15105, typical sample types, testing procedures, and practical answers to frequently asked questions about OTR testing of plastic films and sheets.
Technical Overview
Oxygen transmission rate (OTR), also known as oxygen permeability or oxygen gas transmission rate (OGTR), is defined as the steady-state volume of oxygen that passes through a unit area of a plastic film or sheet per unit time under specified temperature and relative humidity conditions. The most commonly reported unit is cm³/(m²·24 h) at 23 °C and 0% RH or 50% RH. Because oxygen ingress is one of the primary causes of oxidative degradation in packaged products—leading to rancidity in foods, potency loss in pharmaceuticals, and corrosion in electronics—OTR is one of the most widely specified barrier properties in packaging material specifications.
Plastic films differ enormously in their oxygen barrier performance, spanning several orders of magnitude. Low-barrier polyolefin films such as LDPE may exhibit OTR values of several thousand cm³/(m²·24 h), while high-barrier structures containing ethylene-vinyl alcohol copolymer (EVOH), polyvinylidene chloride (PVDC), aluminum foil, or transparent oxide coatings (AlOx, SiOx) can achieve values below 0.5 cm³/(m²·24 h), with foil laminates reaching values below 0.01 cm³/(m²·24 h). Accurate measurement across this wide range requires instrument methods with high sensitivity, well-defined test conditions, and strict control of temperature and humidity.
OTR testing is typically performed by accredited third-party laboratories, in-house quality-control departments, or research and development teams using dedicated permeation analyzers. The results are used for material qualification, supplier verification, shelf-life modeling, packaging structure optimization, and compliance verification against industry and regulatory requirements.
Testing Samples
Monolayer Plastic Films
Single-layer films are the most frequently tested sample type. Common materials include polyethylene (LDPE, LLDPE, HDPE), polypropylene (CPP, OPP, BOPP), polyethylene terephthalate (PET, BOPET), polyamide (nylon 6, BOPA), polyvinyl chloride (PVC), polystyrene (PS), polylactic acid (PLA), and cellophane. Testing monolayer films establishes the baseline barrier contribution of each layer in a packaging structure.
Multilayer and Laminated Films
Flexible packaging structures, such as PET/AL/PE, PET/EVOH/PE, BOPP/CPP, and PA/PE laminates, are tested as finished laminates to determine the real-world barrier performance of the complete structure. Testing of laminated films is essential because adhesives, tie layers, and lamination processes can influence the overall oxygen barrier of the composite.
High-Barrier and Coated Films
High-barrier materials include EVOH films, PVDC-coated films, metallized PET (VMPET), aluminum foil laminates, and transparent barrier films coated with aluminum oxide (AlOx) or silicon oxide (SiOx). These materials require high-sensitivity instruments capable of resolving OTR values below 0.1 cm³/(m²·24 h), and their performance is often strongly dependent on relative humidity.
Rigid and Semi-Rigid Sheets
Thermoforming sheets for trays and containers (for example PP, PET, APET/PE, PS/EVOH/PE sheets), pharmaceutical blister films (PVC, PVDC-coated PVC, PVC/PVDC/PE, PA/Al/PVC tri-laminates), and rigid barrier sheets are also tested. Thicker sheet samples are measured as discs or plaques, and the results can be expressed as a permeability coefficient normalized for thickness.
Coated Papers and Biodegradable Films
Plastic-coated papers, biodegradable films such as PLA and PBAT-based materials, and bio-based barrier coatings are increasingly tested for OTR as converters seek recyclable or compostable alternatives with adequate barrier performance.
Testing Items
Standard OTR test programs for plastic films and sheeting generally include the following measurable items:
- Oxygen transmission rate (OTR) of flat film or sheet samples, expressed in cm³/(m²·24 h) under specified conditions.
- Oxygen permeance, expressed in cm³/(m²·24 h·atm) or mol/(m²·s·Pa), describing the barrier performance of a structure independent of the oxygen partial pressure difference.
- Oxygen permeability coefficient, expressed in cm³·mm/(m²·24 h·atm) or equivalent SI units, used to compare the intrinsic barrier properties of homogeneous materials of different thicknesses.
- OTR at controlled relative humidity (for example 35%, 50%, 85%, or 90% RH) to evaluate humidity sensitivity, which is particularly important for EVOH-containing structures.
- OTR at elevated temperatures (for example 38 °C or 40 °C) for accelerated comparison or tropical climate simulation.
- Oxygen transmission rate of complete packages, bottles, trays, and finished containers, expressed in cm³ per package per 24 h.
- Temperature-dependence studies and Arrhenius activation energy analysis for shelf-life prediction models.
Testing Methods
Coulometric Sensor Method (Equal-Pressure Method)
The coulometric sensor method is the most widely used technique for OTR testing of plastic films and is specified in ASTM D3985, ASTM F1927 (with controlled relative humidity), ISO 15105-2, and GB/T 19789. In this method, the specimen is mounted as a sealed barrier between two chambers. High-purity oxygen (or air) flows on one side of the film, while oxygen-free carrier gas (nitrogen) sweeps the other side. Oxygen molecules that permeate through the film are carried by the nitrogen stream to a coulometric sensor, where they are electrochemically reduced; the resulting electrical current is directly proportional to the oxygen transmission rate. Because both sides of the film are at essentially atmospheric pressure, the method avoids physical distortion of the specimen and allows precise humidity control. Typical test conditions are 23 °C ± 2 °C with 0% RH (dry) or 50% RH, and the method is suitable for OTR values from below 0.01 up to several thousand cm³/(m²·24 h).
Differential-Pressure Method (Manometric Method)
The differential-pressure method, specified in ISO 15105-1, ASTM D1434, GB/T 1038, and JIS K 7126-1, measures gas permeability by sealing the specimen between a high-pressure chamber containing oxygen and an evacuated low-pressure chamber. The increase in pressure (or volume) in the low-pressure chamber is monitored over time and converted into a transmission rate and permeability coefficient. The method does not require a carrier gas or sensor chemicals, can measure a variety of gases (oxygen, nitrogen, carbon dioxide), and is well suited to research on homogeneous materials, although the pressure differential across the specimen may slightly deform very flexible films.
Package-Level (Whole-Container) Testing
For finished packages, ASTM F1307 and related methods measure the oxygen transmission of complete pouches, trays, bottles, or blister packs using a coulometric detector. The package is mounted in a test chamber, oxygen flushes the exterior, and an oxygen-free carrier gas sweeps the interior or headspace so that total ingress through walls, seals, and closures is captured. Package-level results, expressed in cm³ per package per day, are essential for validating seal integrity and overall barrier performance of real containers.
Sample Preparation and Conditioning
Specimens are typically cut as flat, wrinkle-free sheets or discs free of pinholes, wrinkles, and contamination, sealed with vacuum grease or gaskets into the permeation cell, and conditioned prior to testing. Standard conditioning atmospheres per ISO 291 or ASTM D618 (23 °C ± 2 °C, 50% ± 10% RH for at least 40 hours) are commonly applied unless the product specification states otherwise. The test is run until steady-state transmission is reached, and results are reported together with the test temperature, relative humidity, specimen thickness, and the referenced standard. Multi-point measurements on replicate specimens (typically three or more) are recommended to account for material variability.
Applications
OTR testing of plastic films and sheets supports quality control and development across many industries:
- Food packaging: qualification of barrier films for modified atmosphere packaging (MAP), vacuum packaging, oxygen-sensitive products such as nuts, coffee, dairy products, processed meats, and dried foods, and inputs for shelf-life modeling.
- Pharmaceutical packaging: evaluation of blister films, lidding foils, and flexible pouches for tablets and capsules that are sensitive to oxidation, supporting stability studies and regulatory submissions.
- Medical device packaging: verification of sterile barrier systems where oxygen and moisture ingress can compromise device performance and sterility.
- Electronics and display packaging: assessment of high-barrier films for OLED encapsulation, optical films, and moisture- and oxygen-sensitive electronic components.
- Battery and new energy materials: barrier evaluation of packaging films, separator coatings, and aluminum-plastic laminated films for lithium-ion cells.
- Material development and research: comparison of new resins, coatings, biodegradable polymers, and nanocomposite barrier layers, and verification of recycling or down-gauging effects on barrier performance.
- Supplier and incoming inspection: routine verification that purchased films and laminates meet contractual barrier specifications before conversion.
FAQ
What is oxygen transmission rate (OTR) and why is it important?
OTR is the steady-state volume of oxygen that permeates through one square meter of a plastic film or sheet in 24 hours under specified temperature and humidity conditions, usually expressed in cm³/(m²·24 h). It directly determines how quickly oxygen enters a package, which controls oxidative spoilage of food, degradation of pharmaceuticals, and corrosion of sensitive products, making it a decisive parameter for shelf-life and packaging design.
Which test method should be chosen: coulometric or differential-pressure?
The coulometric sensor method (ASTM D3985, ISO 15105-2) is the preferred method for most commercial film testing, especially high-barrier materials and tests requiring controlled humidity. The differential-pressure method (ISO 15105-1, ASTM D1434) is advantageous for multi-gas research measurements and permeability coefficient determination of homogeneous materials. Many accredited third-party laboratories offer both methods and can advise on the most suitable approach for a given material and specification.
What sample size is required for testing?
Most instruments require flat specimens with a diameter of approximately 50 mm to 140 mm depending on the test cell, giving an effective test area between roughly 5 cm² and 100 cm². Samples must be flat, clean, wrinkle-free, and free of pinholes. For package-level testing, the entire finished package is submitted.
Why is relative humidity control important in OTR testing?
Many barrier materials, especially those containing EVOH or polyamide layers, are hydrophilic, and their oxygen barrier performance can degrade dramatically at high humidity—EVOH barrier loss at 85–90% RH can be several-fold compared with dry conditions. Testing at both 0% RH and elevated humidity (for example 50%, 85%, or 90% RH per ASTM F1927) provides a realistic picture of performance in actual distribution environments.
How long does an OTR test take?
For medium-barrier films, steady state is usually reached within a few hours, and a complete test with conditioning may take from several hours to one or two days. High-barrier materials such as foil laminates or thick EVOH structures can take longer because equilibrium transmission is very low. Replicate testing extends the overall schedule accordingly.
What are typical OTR values for common plastic films?
As an indicative guide at 23 °C and dry conditions: aluminum foil laminates typically measure below 0.01 cm³/(m²·24 h); EVOH films around 0.1–2 cm³/(m²·24 h); PVDC-coated films around 1–10 cm³/(m²·24 h); oriented PET around 50–130 cm³/(m²·24 h); biaxially oriented PA around 30–50 cm³/(m²·24 h); BOPP around 1,500–2,500 cm³/(m²·24 h); and LDPE around 7,000–10,000 cm³/(m²·24 h). Exact values depend on thickness, crystallinity, orientation, and test conditions.
What is the difference between OTR, permeance, and permeability coefficient?
OTR is the raw transmission rate through a specific specimen at specific conditions. Permeance normalizes this rate by the oxygen partial pressure difference across the film and describes a structure regardless of the driving force. The permeability coefficient additionally normalizes for material thickness, allowing intrinsic comparison between different homogeneous materials. Reporting the correct parameter depends on whether the sample is a monolayer material or a multilayer structure.
How should OTR results be reported?
A complete report should state the referenced standard (for example ASTM D3985 or ISO 15105-2), the test temperature and relative humidity, specimen identification and thickness, the measured OTR value with units and test area, the number of specimens tested, and the mean and standard deviation. This ensures results are traceable, comparable between laboratories, and suitable for specification compliance decisions.