Water vapor permeability is an important property when evaluating the barrier performance of films, packaging materials and multilayer structures. Measuring water vapor transmission helps determine how effectively a material limits the passage of moisture under defined test conditions.
The Water Vapor Transmission Rate (WVTR) is a key parameter used to characterize water vapor transmission through a material. It provides quantitative data that can support material development, comparison and quality control.
ExtraSolution offers solutions for measuring water vapor transmission and characterizing the barrier properties of films and other materials.
What Is Water Vapor Permeability?
Water vapor permeability describes the ability of water vapor to pass through a material. It is an important property when evaluating materials designed to limit moisture transmission.
The behavior of a material depends on several factors, including its composition, thickness, structure, temperature and relative humidity.
In packaging applications, evaluating water vapor permeability helps characterize materials and compare their performance under defined conditions.
What Is WVTR?
WVTR stands for Water Vapor Transmission Rate. It indicates the amount of water vapor passing through a defined area of material over a given period under specified test conditions.
WVTR is widely used to characterize plastic films, barrier films, laminates and multilayer materials.
In general, a lower WVTR indicates lower water vapor transmission under the conditions used for the test. Results should be compared only when the relevant test conditions and reporting units are consistent.
Why Measure WVTR?
WVTR measurement provides quantitative information about the moisture barrier performance of a material.
This information can be useful to:
- compare different films and packaging materials;
- evaluate moisture barrier performance;
- support the development of new materials;
- assess the effects of changes in thickness or composition;
- qualify materials and suppliers;
- monitor material consistency during quality control.
WVTR testing can therefore support both research and development activities and routine material evaluation.
How Is Water Vapor Permeability Measured?
Water vapor transmission is commonly measured using a permeation cell in which the sample separates two environments with defined humidity conditions.
Water vapor passes through the material, and the instrument detects the transmitted vapor according to the selected measurement method.
The test typically involves:
- preparing and positioning the sample;
- setting the required temperature and humidity conditions;
- measuring the water vapor transmitted through the sample;
- determining the WVTR from the measurement data.
The specific procedure depends on the instrument, the material and the applicable test method. Reliable results require appropriate sample preparation and controlled test conditions.
Which Materials Can Be Tested Using WVTR?
WVTR testing can be used to characterize a wide range of materials in which moisture transmission is an important property.
Typical examples include:
- plastic films;
- barrier films;
- multilayer films;
- laminated materials;
- metallized films;
- co-extruded structures;
- membranes and other technical materials suitable for the selected method.
The appropriate test configuration depends on the material, its structure and the required measurement range.
WVTR and the Barrier Properties of Materials
WVTR is one of the parameters used to characterize the barrier properties of materials.
However, water vapor transmission is different from oxygen or carbon dioxide transmission. A material’s performance should therefore be evaluated according to the specific substance and property of interest.
When selecting a material, it may be necessary to consider several barrier properties, depending on the requirements of the intended application.
Water Vapor Barrier Performance in Films
Plastic films and multilayer structures can exhibit different levels of resistance to water vapor transmission.
Their performance depends on material composition, thickness, layer arrangement and the presence of coatings or other functional layers.
Testing the complete structure makes it possible to compare different material combinations and evaluate the effect of structural changes on moisture barrier performance.
For more information, see Permeability Measurement of Multilayer Films and Laminates.
Factors That Influence WVTR
Several factors can influence the measured WVTR, including:
- Material composition: different materials exhibit different water vapor transmission characteristics.
- Thickness: changes in thickness can affect transmission through the sample.
- Film structure: multilayer films and laminates may behave differently depending on the combination of layers.
- Temperature: temperature can influence water vapor transmission.
- Relative humidity: the humidity conditions on either side of the sample can affect the measurement and the material’s behavior.
- Test method: measurement procedures and test conditions must be considered when interpreting results.
For meaningful comparisons, measurements should be performed under consistent and clearly documented conditions.
WVTR in Packaging Applications
WVTR testing is relevant to packaging materials for which moisture transmission is an important characteristic.
It can be used during material selection, packaging development and quality control to compare films, laminates and other suitable structures.
The appropriate test depends on the material, the intended packaging application and the required barrier performance.
Standards and Test Conditions for WVTR Measurement
WVTR measurements should be performed according to a suitable test method and under defined conditions.
The applicable standard depends on the material, the measurement technique and the requirements of the test.
Temperature, relative humidity, sample preparation and reporting units should be considered when interpreting results or comparing materials.
Where a specific standard is required, the measurement procedure and instrument configuration should be selected accordingly.
How to Choose a WVTR Tester or Analyzer
Selecting a WVTR analyzer starts with identifying the material to be tested and the required measurement range.
Important factors include:
- sample type and dimensions;
- expected WVTR range;
- required temperature conditions;
- relative humidity control;
- number of samples to be tested;
- applicable test methods and standards;
- whether oxygen or carbon dioxide transmission must also be measured.
The most suitable configuration depends on the laboratory’s testing objectives and the characteristics of the materials being analyzed.
ExtraSolution Instruments for WVTR Measurement
ExtraSolution offers solutions for measuring water vapor transmission through films and barrier materials.
Depending on the required measurements, available systems include:
- PermeH2O — for water vapor permeability measurement;
- MultiPerm O2-H2O — for oxygen and water vapor transmission measurements;
- MultiPerm H2O-CO2 — for water vapor and carbon dioxide transmission measurements;
- TotalPerm — for characterizing oxygen, carbon dioxide and water vapor transmission using an integrated system.
The appropriate instrument depends on the measurement requirements, sample characteristics and test conditions.
WVTR and Other Barrier Properties
Depending on the application, water vapor transmission may need to be evaluated alongside other barrier properties.
The main complementary parameters include:
- OTR (Oxygen Transmission Rate), which characterizes oxygen transmission;
- CO₂TR (Carbon Dioxide Transmission Rate), which characterizes carbon dioxide transmission.
Each parameter describes a different transmission characteristic and should be selected according to the requirements of the material and its intended use.
For further information, see:
Measure WVTR with ExtraSolution
ExtraSolution offers solutions for WVTR measurement and the characterization of moisture barrier properties in films and other materials.
Contact ExtraSolution to identify the most suitable configuration for your materials, measurement range and test requirements.
Explore Related Topics
- Gas Permeability: Measurement and Analysis
- Water Vapor Permeability and WVTR: Measurement and Analysis
- Oxygen Permeability and OTR: Measurement and Analysis
- CO₂ Permeability and CO₂TR: Measurement and Analysis
- Barrier Properties of Films: Measurement and Characteristics
- Barrier Films: Characteristics, Materials and Measurement Methods