Packaging barrier performance testing mainly measures two parameters: oxygen transmission rate (OTR) and water vapor transmission rate (WVTR). When reviewing the data, you must consider three things simultaneously—numerical values, test conditions (temperature and humidity), and the test method standard. A test report that only provides a single number without specifying the conditions has no comparative value during material selection.
What does packaging barrier performance testing measure?
Barrier performance describes the rate at which gases or water vapor pass through packaging materials. It is not an inherent property of a material, but rather the result of the interaction between the material’s structure, thickness, temperature, and humidity.
- Oxygen Transmission Rate (OTR)Oxygen transmission rate through the film per unit area per unit time. The lower the value, the stronger the oxygen barrier property.
- Water Vapor Transmission Rate (WVTR)Water vapor mass passing through a unit area of the film per unit time. The lower the value, the stronger the moisture barrier property.
- For products containing oils, nuts, coffee, and baked goods, oxygen is the main enemy; for powdered, crisp, biscuit, and freeze-dried products, water vapor is the main enemy; many products require protection against both.
The selection logic for barrier performance is to work backward: first determine the shelf life and acceptable range of quality changes, then derive the limits of OTR and WVTR based on the sensitivity of the contents, and finally choose the material structure. Reverse operations (selecting materials first and then checking the shelf life) often result in over-packaging or failure to meet the shelf life requirements.
Units and Conversion: Don’t get confused by cm³/(m²·24h·atm)
The most common place where barrier data is prone to errors is inconsistent units. Common writing styles include:
| Project | Common Units | Meaning |
|---|---|---|
| Oxygen Transmission Rate | cm³/(m²·24h·atm) | Oxygen volume passed per square meter per day (pressure difference of 1 atmosphere) |
| Oxygen Transmission Rate | cm³/(m²·24h·0.1MPa) | Almost the same as the previous unit value (1 atm ≈ 0.101325 MPa) |
| Oxygen Transmission Rate (US) | cm³/(100 in²·24h) | 1 cm³/(100 in²·24h) ≈ 15.5 cm³/(m²·24h) |
| Water Vapor Transmission Rate | g/(m²·24h) | Water vapor transmission rate per square meter per day |
| Water Vapor Transmission Rate (US) | g/(100 in²·24h) | 1 g/(100 in²·24h) ≈ 15.5 g/(m²·24h) |
| Uniform Thickness | cm³·µm/(m²·24h·atm)、g·mm/(m²·24h) | Material intrinsic properties are for comparison purposes only and cannot be used to compare finished products. |
Conversion errors are a common cause of selection mistakes. There is a difference of more than 15 times between US units and metric units. If a supplier provides data in US units while the buyer interprets it in metric units, the barrier performance will be misjudged by an order of magnitude.
In addition, it is important to distinguish between material intrinsic values 0 and 1, and finished product values 2 and 3. Normalized thickness data is used for comparing the properties of resin or film materials themselves, but the barrier performance of finished bags depends on the total thickness, layer sequence, adhesive layers, creases, and sealing of the composite structure. These two sets of data cannot be used interchangeably.
Test conditions must be viewed together: temperature and humidity determine the values.
The values of the same film can differ by several times under different conditions, which is the easiest place for barrier data to be misinterpreted.
- Temperature InfluenceTransmittance increases significantly with rising temperature. Empirically, transmittance roughly doubles 1.5 to 2 times for every 10℃ increase in temperature. The actual transmittance of refrigerated products (0–4℃) is typically significantly lower than the test values at 23℃, while products stored at normal temperature (25–35℃) may have higher transmittance than the test values.
- Humidity InfluenceOxygen transmission rate is typically labeled as 23℃/0%RH or 23℃/50%RH, while moisture transmission rate is commonly measured under 38℃/90%RH. For hydrophilic materials (EVOH, nylon), humidity has a significant impact—EVOH’s oxygen barrier performance may decrease by an order of magnitude under high humidity conditions.
- Differences in Testing MethodsThe results may differ when measuring the same film using the constant pressure method and the pressure difference method. The pressure difference method is more sensitive to the sample’s sealing performance, while the constant pressure (Coulomb) method is closer to the actual usage conditions.
Therefore, when making inquiries and comparing prices, it is recommended to uniformly request suppliers to provide data under the same standards and conditions, and to specify the standard number.
Test Methods and Corresponding Standards
| Project | Common Methods | Standard No. | Notes |
|---|---|---|---|
| Oxygen Transmission Rate | Isobaric (Coulomb Sensor) Method | ASTM D3985、ISO 15105-2 | Stable results, most commonly used for flexible packaging |
| Oxygen Transmission Rate | Differential Pressure Method | GB/T 1038、ISO 15105-1 | Suitable for high barrier materials; note that the sample should be sealed. |
| Water Vapor Transmission Rate | Infrared Sensor Method | ASTM F1249、ISO 15106-2 | Fast speed, commonly used for membrane material sampling inspection |
| Water Vapor Transmission Rate | Cup (Weight) Method | GB/T 1037、ISO 15106-1 | Traditional arbitration methods are time-consuming |
| Finished Bag | Headspace residual oxygen, bag leakage | Refer to GB/T 10004 and industry methods | Verify the structure and sealing, not a single-layer film |
It should be emphasized that film data cannot replace finished product data. The barrier performance of the finished bag is also affected by sealing width, creases, and bag type (stress concentration in the bottom pleat area). The permeability in the creased area may be more than 50% higher than that in the flat area.
Common Film Material Barrier Grade Comparison
The following are common reference values (actual data may vary due to differences in thickness, process, and testing conditions, and is provided for reference when selecting the appropriate model).
| Structure (Example) | Oxygen Transmission Rate (OTR) | Water Vapor Transmission Rate (WVTR) Level | Applicable Scenarios |
|---|---|---|---|
| LDPE / PE Single Layer | 1000–2000+ | 8–15 | Short-term moisture protection, no oxygen barrier required |
| BOPP | 1500–2500 | 5–8 | General packaging, expanded food outer bag |
| PET / PE | 50–120 | 8–15 | Regular food, medium shelf life |
| BOPA / PE | 30–50 (dry) | 100–200 | Puncture-resistant priority, products containing bones and shells |
| VMPET / PE (Aluminum Coated) | 1–5 | 1–2 | High barrier, light sensitive |
| PET / EVOH / PE | 0.1–1 (dry) | 3–8 | High Oxygen Barrier, Medium Shelf Life |
| PET/AL/PE (Pure Aluminum) | ≈0（＜0.01） | ≈0 | Long shelf life, extremely high barrier properties, light-sensitive |
From the table, it can be seen that nylon has good oxygen permeability but poor moisture permeability, making it suitable for puncture resistance but not for moisture barrier; metallized film offers good barrier properties at a low cost, but it is prone to pinholes at creases, leading to a deterioration in performance; pure aluminum foil provides almost complete barrier properties, but at the cost of being non-microwaveable and non-recyclable. For specific structural and selection discussions, please refer to this document.High Barrier Packaging Materials InterpretationFor products like coffee and coffee powder that are both oxygen and moisture sensitive, the key changes in barrier requirements after grinding are as follows:Barrier focus for coffee powder packaging。
Six Common Misconceptions
- Only single layer valuesThe finished product is a composite structure, and the adhesive layer, printed surface, and crease will all affect the actual barrier properties.
- Ignore thickness normalizationComparing samples with different thicknesses directly will inevitably lead to incorrect conclusions.
- Ignore sealing and creasesInsufficient sealing width or slight cracks in the fold are common causes of actual failure.
- Provide only one number without any conditions.The moisture permeability can differ by several times between 23℃/50%RH and 38℃/90%RH.
- Only view initial valuesThe barrier performance is reflected only after folding, refrigeration, and at the end of shelf life.
- Infer Shelf Life from Film DataThe shelf life must be validated through accelerated testing with actual products or actual storage testing.
Use test data for selection and shelf life estimation
- Set Internal LimitsInclude the internal control limits for OTR and WVTR in the purchase specification and require test data to be provided for each batch.
- Crease TestThe finished bags should be folded according to specifications before testing, to better simulate the actual circulation condition.
- Distinguish between refrigerated and ambient storageThe equivalent shelf life of the same structure under cold chain and normal temperature conditions may differ by several times, and must be validated separately.
- Accelerated Testing SetupCommon accelerated tests are conducted under conditions of 30℃/65% RH or 40℃/75% RH. A shelf life model is established based on permeability data, and then refined using actual storage data.
- Final Product VerificationFor high-value products, conduct periodic sampling tests on headspace residual oxygen and overall bag leakage to form a closed-loop from the film material to the finished product.
- Focus on the actual performance of aluminum foil structuresAlthough pure aluminum foil has excellent barrier properties, pinholes, sealing contamination, and creases can significantly reduce its actual performance. Related judgment methods are as follows:Aluminum Foil Bag Selection Guide。
FAQ
What is the difference between oxygen transmission rate (OTR) and water vapor transmission rate (WVTR)?
OTR represents the rate at which oxygen permeates through the film, typically expressed in units of cm³/(m²·24h·atm); WVTR represents the rate at which water vapor permeates, usually expressed in units of g/(m²·24h). These two parameters address different degradation mechanisms: oily products are mainly concerned with oxygen permeation, while powders, brittle pieces, and freeze-dried products are primarily concerned with moisture. Many products require control of both.
Why do the barrier properties of the same film show significant differences in different reports?
Due to different testing conditions and methods, the transmittance increases by approximately 1.5 to 2 times for every 10℃ rise in temperature. The water vapor transmission rate can differ by several times between 38℃/90%RH and 23℃/50%RH. There are also systematic differences between the equal pressure method and the pressure difference method, as well as between the infrared method and the cup method. Therefore, comparison data must be based on the same standards and conditions.
Is nylon (PA) film suitable for moisture-proof packaging?
Not suitable. Nylon has advantages in puncture resistance and heat resistance, with moderate oxygen permeability but high moisture permeability, making it a material sensitive to humidity. Products containing bones or shells, or those requiring puncture resistance, are suitable for using nylon as the outer or middle layer, but a moisture barrier layer should be added separately.
Does the oxygen barrier performance of EVOH depend on humidity?
Yes, and the impact is significant. EVOH is a hydrophilic material, and its oxygen barrier performance may decrease by an order of magnitude or more in high humidity environments. Therefore, EVOH is typically sandwiched in the middle, with hydrophobic layers such as PE on both sides to prevent direct contact with high humidity contents or external moisture.
Why does the barrier data of pure aluminum foil bags approach zero yet still allow gas leakage?
Actual failure originates from structural defects rather than the material itself. Contamination in the sealing area, pinholes at creases, and insufficient sealing width can significantly increase the actual permeation rate far beyond the nominal value of the film. Therefore, the pure aluminum foil structure also requires full bag leakage and sealing integrity testing.
How to test the barrier properties of the finished bag?
Do not test only the film. It is recommended to perform headspace residual oxygen testing on finished bags and whole bag leakage testing. If necessary, process the folded areas of the finished bags before measuring permeability. Also conduct periodic sampling to establish a correlation between film material data and finished product data.
What information must be included on a test report?
The data must include test standard number, temperature and humidity conditions, sample specifications and thickness, test method and equipment type, and units. The absence of any of these elements makes the data incomparable with data from other suppliers and unsuitable for setting procurement limits.