ASTM E398 Standard Test Method for Water Vapor Transmission Rate (WVTR) of Sheet Materials Using Dynamic Relative Humidity Measurement
ASTM E398 is a standard test technique for determining the rate of water vapour transfer through a flexible barrier material in a dynamic manner and converting the results to commonly used water vapour transmission (WVT) units. The performance of specimens evaluated using this method is expressed in SI units.
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- Overview
- Scope, Applications, and Benefits
- Test Process
- Specifications
- Instrumentation
- Results and Deliverables
Overview
ASTM E398 is a standardized testing procedure used to determine the Water Vapor Transmission Rate (WVTR), also known as Moisture Vapor Transmission Rate (MVTR), of flexible sheet materials.
ASTM E398 uses a dynamic relative humidity measurement, in contrast to conventional “cup” methods that depend on weighing samples over several days. This method is much quicker and is intended to replicate actual storage conditions in which moisture moves from a package into the surrounding environment without being continuously carried away by dry gas.
Scope, Applications, and Benefits
Scope
ASTM E398 specifies a test method for determining the water vapor transmission rate (WVTR) of sheet materials by measuring changes in relative humidity under dynamically controlled conditions. The method is applicable to flexible and semi-rigid sheet materials and is particularly suited for materials with low to moderate water vapor permeability. The test provides quantitative data on the rate of water vapor passage through a material under specified temperature and humidity gradients, supporting material evaluation, quality control, and performance comparison.
Applications
- Evaluation of moisture barrier properties of packaging films and laminates.
- Testing of construction materials, including membranes, foils, and insulation facings.
- Performance assessment of polymeric sheets and coated materials.
- Quality control in the manufacturing of moisture-sensitive products.
- Research and development of advanced barrier materials.
Benefits
- Provides accurate and reproducible measurement of water vapor transmission rate
- Uses dynamic relative humidity measurement for improved sensitivity and response
- Suitable for low-permeability and barrier-type sheet materials
- Enables comparison of moisture barrier performance across materials
- Supports quality assurance and material development processes
Testing Process
Specimen Preparation
Cut test specimen to the required size; condition as specified in the standard.
1Instrument Setup
Set test temperature and establish dynamic relative humidity conditions.
2Specimen Mounting
Seal the specimen securely between the dry and humid chambers.
3Reporting
Report WVTR with test temperature, humidity conditions, and specimen details.
4Technical Specifications
| Parameter | Details |
|---|---|
| Specimen Type | Flexible or semi-rigid sheet materials |
| Specimen Area | As specified by the test cell design |
| Relative Humidity Gradient | Controlled from a dry to a humid environment |
| Measurement Principle | Change in relative humidity over time |
| Test Duration | Until steady-state WVTR is achieved |
| Output | Water Vapor Transmission Rate (WVTR) |
Instrumentation Used
- Dynamic relative humidity water vapor transmission test chamber
- Controlled temperature and humidity system
- High-precision hygrometers or humidity sensors
- Specimen holder or test cell
- Data acquisition and analysis system
- Airflow control system (if required)
Results and Deliverables
- Water Vapor Transmission Rate (WVTR) expressed in g/m²·day
- Average WVTR value calculated from steady-state measurements
- Test temperature and relative humidity conditions
- Specimen thickness and effective test area
- Number of specimens tested and individual results (if applicable)
- Observations of any test anomalies or deviations from the standard
Frequently Asked Questions
The measurement of WVTR is essential in determining the efficiency of a material used as a vapor barrier. It is also helpful in determining the ability of items such as packaging films, coatings, or membranes to shield products from moisture impacts, which determines product durability and performance in various applications.
The ASTM E398 test method measures the rate of water vapor passage through a sheet material based on a dynamic relative humidity measurement technique. One chamber of the material has a higher humidity, while a sensitive sensor is placed in the other chamber to monitor moisture transmission.
The apparatus has several major constituents: the test cell, clamping arrangement, humidification provision, air source, sensor, data collection system, temperature control, and standard calibration films. Together, these components deliver a reliable WVTR measurement under controlled conditions.
The standard procedure, ASTM E398, is widely applied to flexible barrier materials such as plastic films, coatings, membranes, and packaging. Evaluating the effectiveness of those materials in controlling water vapor transmission finds applications in various fields, from packaging to electronics and, finally, construction.
The factors include leakage from the test seal, improper calibration of the sensor, and variations in humidity. Hence, efforts should be made to eliminate them to a large extent to allow accurate and reproducible measurements.
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