Moisture Vapor Transmission Rate - AbsoluteAstronomy.com

Moisture vapor transmission rate (MVTR), also water vapor transmission rate (WVTR), is a measure of the passage of water vapor through a substance.

There are many industries where moisture control is critical. Moisture sensitive food

Food

Food is any substance consumed to provide nutritional support for the body. It is usually of plant or animal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals...

s and pharmeceuticals are put in packaging with controlled MVTR to achieve the required quality, safety

Safety

Safety is the state of being "safe" , the condition of being protected against physical, social, spiritual, financial, political, emotional, occupational, psychological, educational or other types or consequences of failure, damage, error, accidents, harm or any other event which could be...

, and shelf life

Shelf life

Shelf life is the length of time that food, drink, medicine, chemicals, and many other perishable items are given before they are considered unsuitable for sale, use, or consumption...

. In clothing

Clothing

Clothing refers to any covering for the human body that is worn. The wearing of clothing is exclusively a human characteristic and is a feature of nearly all human societies...

, MVTR as a measure of breathability

Waterproof fabric

Waterproof fabrics are fabrics that are inherently, or have been treated to become, resistant to penetration by water and wetting. They are usually natural or synthetic fabrics that are laminated to or coated with a waterproofing material such as rubber, polyvinyl chloride , polyurethane , silicone...

has contributed to greater comfort for wearers of clothing for outdoor activity. The building material

Building material

Building material is any material which is used for a construction purpose. Many naturally occurring substances, such as clay, sand, wood and rocks, even twigs and leaves have been used to construct buildings. Apart from naturally occurring materials, many man-made products are in use, some more...

s industry also manages the moisture barrier properties in architectural components to ensure the correct moisture levels in the internal spaces of buildings.

Measurement

There are various techniques 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. Note that special care has to be taken in measuring porous substances such as fabrics as some techniques are not appropriate. Likewise for very low levels, many techniques would not have the resolution to provide a reliable result. Numerous standard

International standard

International standards are standards developed by international standards organizations. International standards are available for consideration and use, worldwide...

methods are described in ISO, ASTM, BS

British Standards

British Standards are the standards produced by BSI Group which is incorporated under a Royal Charter...

, DIN

Din

DIN or Din or din can have several meanings:* A din is a loud noise.* Dīn, an Arabic term meaning "religion" or "way of life".* Din is one of the ten aspects of the Ein Sof in Kabbalah ....

etc., -- these are quite often industry-specific. Instrument manufacturers will often be able to provide test methods developed to fully exploit the specific design which they are selling.

The conditions under which the measurement is made has a considerable influence on the result. Both the temperature of and humidity gradient across the sample need to be measured, controlled and recorded with the result. An MVTR result without specifying these conditions is almost meaningless. Certainly no two results should be compared unless the conditions are known.
The most common international unit for the MVTR is g/m²/day. In the USA, g/100in²/day is also in use, which is approximately 1/15 of the value of g/m²/day units. (More precisely, the ratio is 1/15.500031, or very close to 2/31.) Typical rates in aluminium foil laminates may be as low as 0.001 g/m²/day, whereas the rate in fabrics can measure up to several thousand g/m²/day.

Often, testing is conducted on a sheet of material. Calculations based on that can be useful when designing completed structures (packages, clothing, etc.). Seams and seals are also very important to end-use performance; performance verification and validation

Verification and Validation

In software project management, software testing, and software engineering, verification and validation is the process of checking that a software system meets specifications and that it fulfills its intended purpose...

of complete containers or irregular objects is often recommended.

Measurement

See also

External links

Further reading

ASTM Standards