Oxygen Transmission Rate (OTR) Testing of Cling Film: Standards, Methods, and Applications

Oxygen transmission rate (OTR) testing is a critical quality control and performance evaluation method for cling film (plastic food wrap), as oxygen permeability directly determines product freshness, color retention, respiration balance, and shelf life of packaged foods. This article provides a comprehensive technical guide to cling film OTR testing, covering applicable standards such as ASTM D3985, ISO 15105, and GB/T 19789, mainstream testing methods, sample preparation requirements, and typical applications in the food packaging industry.

Technical Overview

Oxygen transmission rate (OTR) is defined as the steady-state volume of oxygen that permeates through a unit area of a packaging material per unit time under controlled temperature, relative humidity, and partial-pressure conditions. For flexible films such as cling film, results are typically expressed in cm³/(m²·24h·0.1 MPa). Because cling film is used extensively for direct food contact applications, including wrapping fresh meat, seafood, produce, and cheese, its oxygen barrier behavior is one of the most decisive properties governing product appearance, microbial growth, and overall shelf life.

Unlike high-barrier laminates, most cling films are intentionally permeable to oxygen. Fresh red meat, for example, requires substantial oxygen ingress to maintain the bright-red oxymyoglobin bloom color expected by consumers, while fresh produce requires a permeability level matched to its respiration rate to prevent anaerobic fermentation. OTR testing therefore serves two purposes: verifying conformity with product specifications and scientifically optimizing film formulations for specific food categories.

The most widely applied test standards include ASTM D3985 (coulometric sensor method for films), ASTM F1927 (humidified conditions), ASTM F1307 (whole packages), ASTM D1434 (differential-pressure method), ISO 15105-1 and ISO 15105-2, GB/T 19789, GB/T 1038, and JIS K 7126. Accredited third-party laboratories routinely perform these tests for compliance verification, supplier qualification, and shelf-life studies.

Testing Samples

Polyethylene (LDPE / LLDPE) Cling Film

Polyethylene-based wraps are the most common household and catering formats, typically produced at gauges of 8–15 µm. Their OTR values are relatively high, often in the range of several thousand cm³/(m²·24h), due to the flexible amorphous structure of polyethylene. Testing confirms both conformity to specification and consistency across production lots.

Polyvinyl Chloride (PVC) Cling Film

PVC cling film, widely used in supermarkets for fresh meat and produce wrapping, is valued for its high oxygen permeability combined with excellent clarity and stretchability. OTR testing verifies that the film delivers the elevated permeability required for red-meat blooming and produce respiration, and that plasticizer loading remains within the intended formulation window.

PVDC, EVA, and Multilayer Cling Films

PVDC-coated and coextruded multilayer wraps provide reduced OTR for products requiring greater oxidative protection, such as cured meats and hard cheese. Because humidity can significantly alter the barrier performance of these structures, testing is frequently performed in both dry (0% RH) and high-humidity states.

Specimen Preparation and Conditioning

Representative, defect-free specimens must be prepared before testing to ensure reproducible results. General requirements include the following:

• Specimens must be flat, wrinkle-free, and free of pinholes, gels, or noticeable thickness variation.
• Condition specimens at 23 ± 2 °C and 50 ± 5% RH for a minimum of 4 hours, or as specified by the applicable standard.
• A minimum of three replicate specimens per material should be tested, with the mean and standard deviation reported.
• Thickness should be measured at multiple points across the specimen, since OTR is thickness-dependent.
• Specimen area exposed to the test gas must be accurately known and free of leaks at the clamping seal.

Testing Items

The core measurable parameters for cling film oxygen permeation evaluation include the following:

• Oxygen Transmission Rate (OTR): the steady-state oxygen flux through unit film area per unit time, the primary reported result.
• Oxygen Permeance: the OTR normalized to the actual oxygen partial-pressure difference across the specimen, expressed in cm³/(m²·24h·0.1 MPa).
• Oxygen Permeability Coefficient: the permeance normalized by film thickness, applicable to homogeneous materials, allowing intrinsic comparison between different resins.
• Humidity-Dependent OTR: permeation behavior measured at elevated relative humidity (for example, 38 °C / 90% RH) to simulate contact with moist foods or distribution in hot, humid climates.

A complete test report should state the test method, temperature, relative humidity, average thickness, specimen area, individual and mean OTR values, standard deviation, and identification of the instrument and standard applied.

Testing Methods

Coulometric Sensor Method (Equal-Pressure Method)

The specimen is clamped as a barrier between two chambers. High-purity oxygen or air flows continuously through one chamber, while oxygen-free nitrogen carrier gas sweeps the other chamber at essentially the same total pressure. Oxygen molecules that permeate through the film are entrained in the nitrogen stream and delivered to a coulometric (fuel-cell) sensor, where the generated electrical current is directly proportional to the quantity of oxygen transported. This method, standardized in ASTM D3985, ISO 15105-2, and GB/T 19789, is generally preferred for high-permeability elastic films such as cling film because it offers a wide measurement range, high sensitivity, and no mechanical stress on thin specimens.

Differential-Pressure Method (Manometric Method)

In this approach, standardized in ASTM D1434, ISO 15105-1, and GB/T 1038, the specimen separates a high-pressure chamber charged with oxygen from an evacuated or low-pressure chamber. The increase in pressure, gas volume, or oxygen quantity on the low-pressure side is monitored over time and converted into the transmission rate. The method enables simultaneous determination of permeability, diffusion, and solubility coefficients through time-lag analysis. Its principal limitation for cling film is that the total-pressure gradient can deform very thin, highly elastic films, so it is more often applied to multilayer and rigid barrier structures.

Standard Test Conditions and Procedure

Regardless of the method selected, a typical OTR determination follows this sequence:

• Stabilize the instrument at the specified condition, most commonly 23 ± 0.5 °C at 0% RH or 50% RH, with optional high-humidity programs such as 38 °C / 90% RH.
• Purge both chambers with high-purity nitrogen to remove residual oxygen and establish a stable zero baseline.
• Introduce the oxygen test gas and monitor the transmission signal until steady state is reached, typically defined as a variation of no more than 2% over a defined interval for high-OTR materials.
• Calculate OTR from the steady-state signal, normalize by exposed area and partial-pressure difference, and average the replicate results.

Applications

OTR test data for cling film support a broad range of industrial and commercial decisions:

• Fresh red meat packaging: verifying that film OTR is sufficiently high, often in excess of 5,000 cm³/(m²·24h), to maintain the oxymyoglobin bloom color demanded at retail.
• Fresh produce wrapping: matching film permeability to product respiration rates to delay anaerobic spoilage, off-odors, and fermentation.
• Cheese and dairy products: controlling moderate oxygen ingress to balance mold inhibition against ripening requirements.
• Modified atmosphere compatibility: confirming that cling film behavior aligns with the intended headspace atmosphere of overwrapped trays.
• Quality control and supplier qualification: manufacturers, retailers, and food processors rely on accredited third-party laboratories for incoming material inspection, lot release, and dispute resolution.
• Research and development: comparing resin grades, plasticizer systems, gauge reductions, and new multilayer structures against performance targets.

FAQ

What OTR value is appropriate for cling film?

There is no single universal target. Wraps for fresh red meat and high-respiration produce typically require OTR values of several thousand cm³/(m²·24h), whereas barrier-oriented multilayer films for cured products may be specified at only tens to hundreds of cm³/(m²·24h). The correct value depends on the food category, target shelf life, and intended storage conditions.

Which test method is best suited to cling film?

The coulometric equal-pressure method described in ASTM D3985, ISO 15105-2, and GB/T 19789 is generally preferred, because it measures thin, elastic, high-permeability films accurately without subjecting them to a damaging total-pressure gradient. The differential-pressure method is useful when diffusion and solubility coefficients are also required.

How long does an OTR test take?

For high-permeability materials such as PE and PVC cling film, steady state is often reached within thirty minutes to a few hours. Low-permeability multilayer structures may require many hours or even days. Specimen conditioning time is additional and should be planned in advance.

Why is relative humidity control important?

Hydrophilic polymers and plasticized PVC exhibit strong humidity dependence. Elevated humidity can plasticize the polymer matrix and increase OTR substantially, so testing under realistic humidity conditions provides data that better represents actual performance on moist foods.

Can finished wrapped packages be tested instead of flat film?

Yes. Whole-package oxygen transmission can be measured using package-format adaptations of the coulometric method, such as ASTM F1307 or the corresponding package mode of ISO 15105-2. This approach validates the combined effect of film permeability, overlaps, and sealing geometry in real-use conditions.

How should OTR results be interpreted?

Results should always be interpreted against the specification for the intended application, taking into account the reported test temperature, relative humidity, and film thickness. Comparisons between materials are valid only when these test parameters are consistent, which is why standardized reporting and testing through accredited third-party laboratories are strongly recommended.