Abstract

The Water Vapor Transmission Rate (WVTR) is a critical parameter for evaluating the barrier properties of thin sheet 

materials, such as films, membranes, and packaging materials. ISO 2528 specifies a gravimetric method for determining 

WVTR by measuring the mass change of a test specimen exposed to controlled humidity conditions. This article outlines 

the principles, apparatus, test procedure, and calculations involved in the gravimetric determination of WVTR in accordance

 with ISO 2528.

1. Introduction

The ability of a material to resist or allow the passage of water vapor is essential in industries such as food packaging, 

pharmaceuticals, and construction. WVTR measures the quantity of water vapor that permeates through a unit area of 

a material over a specified time under defined temperature and humidity conditions. The gravimetric method (or cup 

method) described in ISO 2528 is a widely accepted technique due to its simplicity and reliability.

2. Principle of the Gravimetric Method

The test involves sealing a test specimen over a permeation cup containing a desiccant (for moisture absorption) or a

 saturated salt solution (for moisture release). The assembly is placed in a controlled environment (constant temperature 

and humidity), and the change in mass is measured over time. The WVTR is calculated based on the steady-state rate of

 mass change.

testing instrument：Water Vapor Permeability Tester

3. Test Procedure

3.1 Preparation of Test Specimens

Cut the sheet material into circular specimens that fully cover the cup opening.

Condition specimens at standard atmosphere (23°C, 50% RH) if required.

3.2 Assembly of Permeation Cups

Fill the cup with desiccant (for moisture absorption tests) or a saturated salt solution (for moisture emission tests).

Seal the test specimen over the cup opening using an adhesive or wax to prevent edge leakage.

3.3 Conditioning and Weighing

Place the assembled cups in a controlled environment (e.g., 23°C and 85% RH for high humidity testing).

Weigh the cups at regular intervals until a steady-state mass change rate is achieved (typically over several days).

4. Factors Affecting WVTR Measurements

Temperature and humidity (must be strictly controlled)

Sealing integrity (leakage leads to erroneous results)

Thickness and homogeneity of the test material

Equilibration time (steady-state conditions must be reached)

5. Applications and Industry Relevance

Food Packaging: Ensures moisture barrier properties extend shelf life.

Pharmaceuticals: Protects hygroscopic drugs from moisture degradation.

Construction Materials: Evaluates water resistance of membranes and coatings.

6. Conclusion

The gravimetric method per ISO 2528 provides a reliable and standardized approach for measuring WVTR in sheet 

materials. By maintaining strict control over test conditions and ensuring proper sealing, accurate and reproducible 

results can be obtained, aiding in material selection and quality control.