Oxygen transmission rate (OTR) testing quantifies the amount of oxygen that permeates through packaging bag materials or finished packages under controlled temperature and humidity conditions, providing critical data for barrier material selection, shelf-life design, and quality control. This article explains the measurement principles, major international standards such as ASTM D3985, ASTM F1307, ISO 15105, and GB/T 19789, sample requirements, test procedures, and typical applications of packaging bag OTR determination.
Technical Overview
Oxygen transmission rate (OTR) refers to the steady-state volume of oxygen that permeates through a unit area of a packaging material, or through an entire finished package, per unit time under specified temperature and relative humidity conditions. For flat films and sheets, OTR is typically expressed in cm³/(m²·24h·0.1MPa), while for finished packaging bags it is expressed in cm³/(pkg·24h), reflecting the total oxygen ingress through the material body, seals, closures, and other structural features.
Oxygen ingress is one of the most important factors limiting the shelf life of packaged products. In food packaging, oxygen drives lipid oxidation, vitamin degradation, flavor loss, color change, and the growth of aerobic microorganisms. In pharmaceutical and medical packaging, oxygen can compromise active ingredients, biologics, and sterile barrier performance. Determining the OTR of packaging bags therefore allows manufacturers to match barrier performance with product sensitivity, validate shelf-life claims, and monitor incoming material quality.
The oxygen barrier performance of a packaging bag depends on multiple factors, including the multilayer structure and thickness of the laminate, the crystallinity and orientation of the polymer layers, the presence of high-barrier components such as aluminum foil, metallized films, EVOH, PVDC, or inorganic oxide coatings, the quality of heat seals and closures, and the ambient temperature and humidity. Because hydrophilic barrier polymers such as EVOH and polyamide are strongly humidity-dependent, OTR must always be reported together with the test temperature and relative humidity.
Testing Samples
Flat Film and Laminate Samples
Representative specimens are cut from roll stock or from the body material of finished bags, free of wrinkles, folds, pinholes, visible defects, and printed ink anomalies. Specimens are typically conditioned at (23 ± 2)°C and (50 ± 5)% relative humidity for a defined period before testing, in accordance with conditioning standards such as GB/T 2918 or ASTM D618.
Finished Packaging Bags
Complete bags, including stand-up pouches, three-side-seal pouches, vacuum bags, retort pouches, zipper pouches, and spouted pouches, can be tested as whole packages. Whole-bag testing captures the combined contribution of the body material, heat seals, zipper closures, spouts, and valve fittings, and is highly effective at revealing seal defects and structural weak points that flat-film testing cannot detect.
Specialty Barrier Structures
High-barrier laminates such as PET/AL/PE, PET/VMPET/PE, PET/EVOH/PE, and paper/AL/PE structures are frequently tested to verify ultra-low transmission values, often below 0.5 cm³/(m²·24h). Such measurements require high-sensitivity instrumentation and rigorous leak-free mounting of the specimen.
Testing Items
Common test items for packaging bag OTR determination include:
- Oxygen transmission rate of flat film or laminate at (23 ± 2)°C, dry condition (0% RH)
- Oxygen transmission rate under controlled humidity conditions, such as 23°C/50% RH, 38°C/50% RH, or 38°C/90% RH, to evaluate humidity sensitivity of barrier layers
- Oxygen transmission rate of finished bags in cm³/(pkg·24h), covering the complete package
- Oxygen permeance and, where required, the oxygen permeability coefficient of the material, calculated by normalizing for specimen thickness
- Comparative or accelerated studies at elevated temperatures to support shelf-life estimation and Arrhenius-based extrapolation
Testing Methods
Coulometric (Equal-Pressure) Sensor Method
The coulometric sensor method is the most widely used technique for OTR determination and is standardized in ASTM D3985, ASTM F1927, ISO 15105-2, and GB/T 19789. The specimen is clamped between two chambers of a permeation cell. One side is swept by oxygen or air, while the other side is swept by oxygen-free nitrogen carrier gas. Oxygen molecules that permeate through the specimen are transported by the carrier gas to a coulometric sensor, where they are electrochemically reduced and generate an electrical current directly proportional to the oxygen flow rate according to Faraday's law. Once the signal reaches steady state, the OTR is calculated. Modern instruments offer detection limits down to approximately 0.001 cm³/(m²·24h) and support relative humidity control of both gas streams, making the method suitable for both routine quality control and high-barrier material qualification.
Differential-Pressure (Manometric) Method
The differential-pressure method, standardized in ASTM D1434, ISO 15105-1, and GB/T 1038, seals the specimen as the divider between two chambers. Both sides are evacuated, and then pure oxygen at a defined pressure is introduced to the high-pressure side. Oxygen permeating the specimen increases the pressure on the low-pressure side, and the OTR is derived from the pressure-versus-time curve. This method does not require carrier gas and is well suited to medium- and high-transmission materials, although careful leak checking and outgassing control are essential for accurate low-barrier-level results.
Finished Package (Whole-Bag) Method
For finished packaging bags, the whole-package method described in ASTM F1307 and GB/T 31358 is applied. The bag is mounted on a custom fixture with inlet and outlet ports installed through a sealed interface, the interior is purged with nitrogen carrier gas, and the exterior of the bag is surrounded by oxygen or air. The total oxygen entering the bag per day is measured and reported in cm³/(pkg·24h). This approach evaluates the real-world barrier performance of the complete package, including seals, corners, gussets, closures, and any secondary components.
Standard Test Conditions
Unless otherwise specified, tests are performed at (23 ± 2)°C with dry gases (0% RH). Humidified testing, typically at 50% RH or 90% RH, is strongly recommended whenever the barrier layer contains EVOH, polyamide, or other humidity-sensitive polymers, since OTR at high humidity may be one to two orders of magnitude higher than the dry value. All results must state the test temperature, relative humidity, and specimen area or package configuration to be comparable.
Applications
Food and Beverage Packaging
OTR data are fundamental to the design of packaging for oxygen-sensitive foods such as roasted coffee, nuts and dried fruits, snack foods, fat-rich bakery products, processed meats under modified atmosphere, and milk powder. By combining measured OTR with headspace oxygen, package geometry, and product oxygen tolerance, manufacturers can calculate allowable oxygen doses and validate best-before dates.
Pharmaceutical and Medical Packaging
Composite bags and films for tablets, capsules, granules, and moisture- and oxygen-sensitive drug products are tested against pharmacopoeial and national packaging standards to confirm barrier compliance. OTR testing also supports the qualification of sterilizable pouches and the selection of materials for oxygen-sensitive active ingredients and biological products.
Industrial and Specialty Packaging
Electronics components, battery materials, chemical reagents, and metal parts susceptible to oxidation are protected by high-barrier bags, frequently incorporating foil or metallized layers. OTR verification confirms that the selected structure, thickness, and sealing design meet the required barrier class.
Quality Control, R&D, and Supplier Verification
Accredited third-party laboratories and in-house QC departments use OTR testing for incoming material inspection, batch release, comparison of alternative laminate designs, evaluation of retort or sterilization processing effects on barrier performance, root-cause analysis of shelf-life failures, and generation of data for regulatory submissions and customer specifications.
FAQ
What units are used to express the oxygen transmission rate of packaging bags?
Flat film and laminate OTR is normally expressed in cm³/(m²·24h·0.1MPa) at the stated temperature and relative humidity. Finished-package OTR is expressed in cm³/(pkg·24h) because the result represents the entire bag rather than a unit area of material.
What is considered a high-barrier packaging bag?
As a general industry convention, materials with OTR below approximately 1 cm³/(m²·24h) are regarded as high barrier, foil-containing laminates often achieve values below 0.5 or even 0.1 cm³/(m²·24h), while common commodity films such as BOPP or PE can range from several hundred to several thousand cm³/(m²·24h).
Why test the whole bag instead of only the film material?
Film testing characterizes the raw material, but oxygen can also enter through heat seals, zipper closures, spouts, corners, and microscopic leaks. Whole-bag testing measures the actual oxygen ingress of the finished package and is the most direct indicator of real-world shelf-life performance.
How does humidity affect OTR results?
Hydrophilic barrier polymers such as EVOH and nylon absorb water at high relative humidity, which plasticizes the polymer chain structure and dramatically increases oxygen permeability. Testing at both dry and high-humidity conditions, for example 23°C/0% RH and 38°C/90% RH, provides a realistic picture of performance across distribution environments.
How long does an OTR test take?
Test duration depends on the barrier level. Medium- and low-barrier materials typically reach steady state within a few hours, whereas ultra-high-barrier foil laminates may require 24 hours or longer to equilibrate and achieve a reliable steady-state value.
How should samples be prepared before testing?
Specimens must be flat, defect-free, and fully representative of production material. They should be conditioned under standard laboratory atmosphere, mounted with leak-free edge sealing, and verified for absence of pinholes and channel leaks. For whole-bag tests, bags should be sealed under controlled conditions, and the fixture interface must be confirmed gas-tight before the measurement begins.