ASTM F1249 Water Vapor Transmission Rate through Plastic Films and Sheets

Developed by the American Society for Testing and Materials (ASTM),ASTM F1249, "Standard Test Method for Water Vapor Transmission Rate through Plastic Films and Sheets Using a Modulated Infrared Sensor," describes a test method for determining water vapor transmission rates through flexible barrier materials. This method is applicable to sheets and films up to 3 mm thick, composed of single or multilayer synthetic or natural polymers and foils, including coated materials. This standard provides determinations of water vapor transmission rate, film permeability to water vapor, and the water vapor permeability coefficient for homogeneous materials. Water vapor permeability and water vapor permeability values ​​should be used with caution. The inverse relationship of water vapor transmission rate to thickness and the direct relationship of water vapor transmission rate to water vapor partial pressure difference may not always be valid.

For the purposes of this standard, the following terms and definitions apply:

• The water vapor permeability coefficient is the product of permeability and film thickness. Permeability is only meaningful for homogeneous materials, in which case it is a property of the bulk material. This quantity should not be used unless the relationship between thickness and permeability has been verified in tests using various material thicknesses.
• Water vapor permeability is the ratio of a barrier's water vapor transmission rate to the vapor pressure difference between two surfaces. Because a sample's permeability is generally a function of relative humidity and temperature, test conditions must be specified.
• The water vapor transmission rate is the time rate of water vapor flow per unit area perpendicular to surfaces under steady-state conditions. When humidity is the difference in relative humidity between samples, the relative humidity and temperature test conditions should be specified.

During the test, a dry chamber is separated from a wet chamber of known temperature and humidity by the barrier material to be tested. The dry chamber and wet chamber form a diffusion cell, enclosed by the test film. Water vapor emitted from the film mixes with the gas in the dry chamber and is carried to a pressure-modulated infrared sensor. This sensor measures the fraction of infrared energy absorbed by the water vapor and generates an electrical signal whose amplitude is proportional to the water vapor concentration. The amplitude of the electrical signal generated by the test film is then compared to a signal generated by measuring a calibration film with a known water vapor transmission rate. This information is then used to calculate the rate at which moisture is transmitted through the test material.

The purpose of this test method is to obtain reliable values ​​for the water vapor transmission rate of plastic film and sheet. Water vapor transmission rate is an important property of packaging materials and can often be directly related to the shelf life and stability of the packaged product.

Data obtained from this test method are suitable for use as a referee testing method if the buyer and seller agree on sampling procedures, standardization procedures, test conditions and acceptance criteria.

The ASTM F1249 standard is essential because it provides a reliable and standardized method for measuring the water vapor transmission rate of plastic films and sheets, which is critical in many industries (especially packaging). Here are a few reasons why it is considered so important:

• Maintaining product quality: Many products, especially food, pharmaceuticals, and electronics, are sensitive to moisture. Too much water vapor passing through packaging can cause spoilage, deterioration, or failure.
• Material comparison: This standard allows manufacturers and researchers to consistently and accurately compare the barrier properties of materials and assists in materials selection and development.
• Quality control and compliance: Provides a repeatable testing method to ensure materials meet regulatory or industry-specific barrier requirements.
• Design optimization: Knowing the water vapor transmission rate helps designers create packaging that balances cost, performance, and shelf life expectations.
• Instrument-based sensitivity: The method described in the ASTM F1249 standard uses an infrared sensor and is known for its high sensitivity and precision, making it suitable for high-performance barrier materials.

In short, the ASTM F1249 standard provides consistency, reliability, and performance benchmarking for moisture barrier properties in materials where water vapor permeability is a critical factor.

Our organization, which has been supporting businesses across all sectors for years through a wide range of testing, measurement, analysis, and evaluation activities, has a strong team of employees who closely follow global developments in science and technology and are constantly improving themselves. In this context, we also provide testing services in accordance with the "ASTM F1249 Standard Test Method for Water Vapor Transmission Rate through Plastic Films and Sheets Using a Modulated Infrared Sensor."