Comparison of Coulometric and Gravimetric Methods for Measuring Material Permeability

Permeability is a critical property that determines a material’s ability to allow gases or liquids to pass through its structure. This factor is essential in a wide range of industries, although food packaging is one of the most important because controlling gas exchange is critical for maintaining product quality and shelf life.

There are several methods to measure permeability, but we will focus on the coulometric and gravimetric methods. In this article, both approaches are described in detail, their applications, and the advantages and disadvantages of each one.

Coulometric Method

The coulometric method directly measures the amount of gas or vapor passing through a material under controlled conditions. Sensors are used to quantify the concentration of the permeated gas, thus making it possible to accurately calculate the material’s permeability.

Key Features of the Coulometric Method:

• Direct Gas Flow Measurement: This method provides high sensitivity, particularly for materials with low permeability, where even small amounts of gas can be detected.
• Fast, Accurate Results: This makes it widely used in the food, pharmaceutical and electronics packaging industries, among others, where preventing gas and vapor penetration is critical.
• Strict Testing Conditions: Temperature and humidity must be carefully controlled and frequent calibrations are necessary to maintain accuracy.

Gravimetric Method

The gravimetric method measures a material’s permeability by observing changes in its mass as it absorbs or releases gas or vapor. The amount of gas permeated is calculated based on this weight variation.

Key Features of the Gravimetric Method:

• Weight-Based Measurement: Instead of directly measuring gas flow, it assesses changes in the material’s mass.
• Simplicity and Cost-Effectiveness: This method does not require specialized equipment, making it more economical and accessible.
• Less Accuracy: It is better suited for porous and highly permeable materials such as textiles, plastics and construction materials.
• Longer Testing Times: The measurement process can take longer, as it depends on the amount of gas absorbed or released by the material.

Which Method is Best for You?

The choice of the coulometric or gravimetric method largely depends on the type of material being analysed and the required level of accuracy.

AIMPLAS Expertise

At AIMPLAS, we can assist with both methods. For the coulometric method, we can measure the permeability of oxygen (O₂) in accordance with standards ASTM D3985 and ASTM F1927, as well as water vapor permeability in accordance with ASTM F1249. We offer testing for films and other packaging.

If you need these measurements or advice on selecting the best method and conditions for your materials, feel free to contact us—we are ready to help!