Water Vapor Transmission Rate (WVT)

Definition - What does Water Vapor Transmission Rate (WVT) mean?

The water vapor transmission rate (WVTR) is a measure of the passage of water vapor through a substance per unit time and unit area. In almost all industrial processes, controlling the water vapor transmission rate is important because moisture may lead to corrosion of industrial equipment or metallic structures.

Water vapor transmission rate (WVTR) is also known as moisture vapor transmission rate (MVTR).

Corrosionpedia explains Water Vapor Transmission Rate (WVT)

Moisture control is important in many industries. Moisture sensitive foods and pharmaceuticals are put in packaging with a controlled MVTR to achieve the required quality, safety and shelf life. Similarly, the building materials industry also manages the moisture barrier properties of architectural components to ensure the correct moisture levels in the building's internal spaces.

There are various tools to measure MVTR, ranging from gravimetric techniques that measure the gain or loss of moisture by mass, to highly sophisticated instrumental techniques that in some designs can measure extremely low transmission rates.

Special care is taken when measuring porous substances such as fabrics because some techniques are inappropriate, and for very low transmission rates because some techniques do not have enough resolution to provide a reliable result.

Numerous standard methods are described in ISO, ASTM, BS and DIN, and these are quite often industry-specific. Instrument manufacturers frequently provide test methods to fully exploit the specific design that they are selling.

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