Moisture vapor transmission rate (MVTR), or water vapor transmission rate (WVTR), is a measure of the passage of moisture or water vapor through a substance. With this method, the permeability of vapor barriers is determined.
There are many industries where moisture control (vapor permeability) is critical. Moisture sensitive foods and medicines are packaged with controlled moisture vapor transmission rate to achieve the desired quality, safety and shelf life. In the textile industry, moisture vapor transmission rate as a measure of breathability contributes to people's comfort. Additionally, the building materials industry manages moisture barrier properties in architectural components to ensure accurate humidity levels in interior spaces of buildings. Organic material-based optoelectronic devices, often called OLEDs, require encapsulation with low water vapor transmission rate values to guarantee the same performance throughout the life of the device. Essentially, the moisture vapor transmission rate decreases with increasing film or barrier thickness and increases with increasing temperature.
To measure moisture vapor transmission rate, gravimetric techniques that measure moisture gain or loss relative to mass are used, as well as highly complex instrumental techniques that can measure extremely low transmission rates in some designs. However, for very low levels most techniques do not have sufficient resolution.
The conditions in which the tests are performed have a significant impact on the result. Both temperature and humidity gradients need to be measured, controlled and recorded in the sample under test. Additionally, the thickness of the sample must be the same. Without specifying these conditions, the results do not mean much. For example, the effect of temperature on permeability can be as high as 10 percent per degree, causing results obtained at 23 and 37 degrees to differ by a factor of 4.
Many international organizations, such as the International Standards Organization (ISO), the American Society for Testing and Materials (ASTM), and the Technical Association of the Pulp, Paper and Converting Industries (TAPPI), have developed numerous standards for measuring moisture vapor transmission rate, and these are often industry-specific.
In short, most flexible packaging is designed to store its contents and protect it from the harmful effects of moisture. The amount of protection is indicated in part by the moisture vapor transmission rate of the material. This value is typically expressed as g/2 per 24/100 hours. The best barrier materials currently on the market have moisture vapor transmission rates greater than 2 g/24 per 0,02/100 hours.
Among the numerous testing, measurement, analysis and evaluation studies provided to businesses by our organization, there are also MVTR moisture vapor transmission rate test services.
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