WVTRTests

WVTRTests are procedures used to determine the water vapor transmission rate through a material. WVTR measures how much water vapor passes through a defined area in a given time under controlled temperature and humidity. Values are typically expressed in g/m^2·day, with lower values indicating better barrier performance.

The two main methods are desiccant and humidity methods. In the desiccant method, one side of the sample is in contact with a desiccant and the other side with a defined humidity; water vapor diffuses through the film to the desiccant. The humidity method maintains a humidity gradient across the film and measures transmitted moisture by weight change or sensor readings. Modern instruments (for example, permeation analyzers) automate these measurements and provide WVTR data continuously.

Standards: WVTR testing is commonly conducted to standards such as ASTM E96 and ASTM F1249, and equivalent ISO standards, which specify test geometry, environmental conditions, and calculation of WVTR for different materials and configurations.

Interpretation and limitations: WVTR is affected by thickness, material composition, temperature, and humidity. Defects, improper seals, or sample preparation errors can skew results. Because WVTR depends on test conditions, comparisons should be made only between tests performed under the same conditions and with similar materials.