Test method for measuring WVTR through plastic film and sheeting using modulated infrared sensor technology
1. Principles and Scope
1.1 Method Description
ASTM F1249 establishes a standardized procedure for measuring water vapor transmission rate (WVTR) through plastic film and sheeting materials. The test employs a modulated infrared sensor to detect water vapor permeation across a specimen maintained at specific temperature and humidity conditions.
The apparatus, typically a MOCON PERMATRAN-W instrument, creates a controlled humidity gradient across the test film. Water vapor diffuses through the material and is quantified by infrared detection, eliminating the time-consuming gravimetric approaches used in earlier methods.
The standard applies to films, sheeting, laminates, coextrusions, and other plastic materials used in packaging and protective applications. Results are reported as grams per square meter per day (g/m²/day).
1.2 Comparison with Related Standards
| Standard | Method Type | Key Characteristic | Measurement Time |
|---|---|---|---|
| ASTM F1249 | Infrared sensor | Modulated IR detection, rapid results | Rapid (hours) |
| ASTM E96 | Gravimetric cup method | Traditional wet cup or dry cup assembly | Slow (days to weeks) |
| ISO 15106-2 | Infrared sensor (ISO equivalent) | International standard, comparable to F1249 | Rapid (hours) |
| ISO 2528 | Gravimetric dish method | Desiccant-based gravimetric approach | Moderate (days) |
2. Role in Evaluation
2.1 Primary Purpose
ASTM F1249 quantifies the permeability of plastic materials to water vapor, enabling manufacturers to select materials suitable for moisture-sensitive applications. The method provides critical data for predicting product shelf life and efficacy under specified storage conditions.
Water vapor transmission rate directly impacts product stability, especially for pharmaceuticals, food items sensitive to moisture uptake or loss, and electronics. The infrared measurement approach accelerates development timelines compared to traditional gravimetric methods.
2.2 Quality Control and Material Selection
Quality control laboratories use ASTM F1249 to monitor batch-to-batch consistency of film and sheeting materials. The rapid measurement capability allows quick feedback during production and facilitates comparison across suppliers and formulations.
Material engineers employ WVTR data to evaluate barrier coatings, multilayer structures, and novel resin formulations. The standard supports design verification for moisture-barrier specifications in packaging specifications and regulatory documentation.
2.3 Limitations and Considerations
Important limitations to recognize:
- Results reflect steady-state conditions at 37.8°C and 100% RH gradient; actual use conditions may differ significantly
- Test measures vapor transmission only; does not address liquid water permeation or oxygen transmission
- Material properties may vary with humidity and temperature history prior to testing
- Sealed laminate structures may be damaged during test apparatus assembly, compromising barrier function
- Pinhole defects or surface contamination can yield anomalously high WVTR values not representative of bulk material
3. Test Procedure
3.1 Specimen Preparation
Test specimens are cut from the material to fit the apparatus measurement cell, typically 50 cm² or as specified by the instrument design. Specimens must be free of visible defects, wrinkles, and contamination that could artificially increase vapor transmission rates.
Materials are conditioned at specified temperature and humidity (usually 23°C and 50% RH) for a minimum period before testing to establish equilibrium moisture content. Laminate structures are assembled and sealed according to material specifications to prevent delamination or edge moisture ingress during testing.
3.2 Execution and Measurement
The specimen is mounted in the test apparatus to establish a defined geometry across which water vapor transmission is measured. One side of the specimen is exposed to dry carrier gas (typically nitrogen), while the other side is exposed to saturated water vapor at 37.8°C.
The modulated infrared sensor detects water vapor accumulated in the dry side of the cell. As water vapor diffuses through the material, the sensor signal increases proportionally. Data acquisition systems record the transmission rate over time until steady-state conditions are established, typically after 30 minutes to 2 hours depending on material permeability.
The system calculates WVTR in g/m²/day based on the steady-state transmission flux and the known area of the test specimen.
3.3 Typical WVTR Values by Material
| Material | WVTR (g/m²/day) | Barrier Classification |
|---|---|---|
| Low-density polyethylene (PE-LD) | ~15 | Moderate barrier |
| Polypropylene (PP) | ~6 | Moderate barrier |
| Polyethylene terephthalate (PET) | ~12 | Moderate barrier |
| Polyamide (PA/Nylon) | ~150 | Low barrier (hydrophilic) |
| Ethylene vinyl alcohol (EVOH) dry conditions | ~3 | High barrier |
| Polyvinylidene chloride (PVdC) | ~1.5 | High barrier |
| AlOx-coated PET | ~0.5 | Ultra-high barrier |
| Aluminum foil | <0.01 | Complete barrier |
4. Regulatory Framework
4.1 Standards References and Context
ASTM F1249 is published by ASTM International (formerly American Society for Testing and Materials) as a consensus standard for moisture barrier evaluation. The standard is maintained in alignment with parallel ISO 15106-2, which establishes equivalent test procedures for international commerce.
Regulatory agencies including the U.S. FDA recognize ASTM F1249 as an acceptable analytical method for supporting shelf-life claims and moisture protection specifications for pharmaceutical and food packaging applications.
4.2 Applications by Industry Sector
Food Packaging
Food manufacturers select barrier films based on WVTR data to prevent moisture migration that would compromise product quality, texture, or shelf life. Snack foods, confections, dried fruits, and powdered products require films with WVTR values typically below 5 g/m²/day to maintain acceptable shelf life. ASTM F1249 data informs material selection for both primary films and laminate structures.
Pharmaceutical Packaging
Blister packs, bottle closures, and protective films in pharmaceutical applications must limit moisture ingress to preserve drug potency and stability. ASTM F1249 measurements validate that selected films meet moisture transmission specifications. Ultra-high barrier materials (WVTR <1 g/m²/day) are common for moisture-sensitive actives and are routinely specified in drug master files.
Electronics and Moisture-Sensitive Devices
Electronic components, photonic devices, and semiconductor assemblies require protective packaging with minimal moisture transmission. ASTM F1249 data ensures packaging films provide adequate protection during storage and transportation. Materials with WVTR below 1 g/m²/day are typical specifications for sensitive electronic devices.
5. Best Practices and Recommendations
5.1 Laboratory Setup and Operation
Laboratories performing ASTM F1249 testing must maintain equipment in proper working condition with regular calibration using reference materials. The MOCON PERMATRAN-W or equivalent instrument should be verified periodically against known standards to ensure accuracy and reproducibility.
Environmental controls in the testing laboratory are critical. Temperature stability within ±1°C and controlled humidity for specimen conditioning prevent anomalous results. Test specimens should be handled with clean gloves to avoid surface contamination that would artificially elevate measured WVTR values.
5.2 Recommendations for Material Evaluation
When evaluating new materials or formulations, conduct ASTM F1249 testing in conjunction with ASTM D3985 (oxygen transmission rate) to establish complete barrier properties. These complementary methods provide the barrier specification profile required for predicting long-term product stability.
For materials with very low WVTR values (below 0.1 g/m²/day), validate results using alternative gravimetric methods such as ASTM E96 to confirm the infrared measurement. Some high-barrier materials approach detection limits of infrared systems, and cross-validation ensures data reliability.
Document all test conditions, environmental parameters, and equipment calibration status to support regulatory submissions and to enable troubleshooting if results diverge from expected material behavior.