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

vapor barrier A vapor barrier (or vapour barrier) is any material used for damp proofing, typically a plastic or foil sheet, that resists diffusion of moisture through the wall, floor, ceiling, or roof assemblies of buildings and of packaging to prevent inter ...

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

food Food is any substance consumed by an organism for Nutrient, nutritional support. Food is usually of plant, animal, or Fungus, fungal origin and contains essential nutrients such as carbohydrates, fats, protein (nutrient), proteins, vitamins, ...

s and

pharmaceutical Medication (also called medicament, medicine, pharmaceutical drug, medicinal product, medicinal drug or simply drug) is a drug used to diagnose, cure, treat, or prevent disease. Drug therapy ( pharmacotherapy) is an important part of the ...

s are put in

packaging Packaging is the science, art and technology of enclosing or protecting products for distribution, storage, sale, and use. Packaging also refers to the process of designing, evaluating, and producing packages. Packaging can be described as a coo ...

with controlled MVTR to achieve the required

quality Quality may refer to: Concepts *Quality (business), the ''non-inferiority'' or ''superiority'' of something *Quality (philosophy), an attribute or a property *Quality (physics), in response theory *Energy quality, used in various science discipli ...

safety Safety is the state of being protected from harm or other danger. Safety can also refer to the control of recognized hazards in order to achieve an acceptable level of risk. Meanings The word 'safety' entered the English language in the 1 ...

, and

shelf life Shelf life is the length of time that a commodity may be stored without becoming unfit for use, consumption, or sale. In other words, it might refer to whether a commodity should no longer be on a pantry shelf (unfit for use), or no longer on a s ...

. In

clothing Clothing (also known as clothes, garments, dress, apparel, or attire) is any item worn on a human human body, body. Typically, clothing is made of fabrics or textiles, but over time it has included garments made from animal skin and other thin s ...

, MVTR as a measure of breathability has contributed to greater comfort for wearers of clothing for outdoor activity. The

building material Building material is material used for construction. Many naturally occurring substances, such as clay, rocks, sand, wood, and even twigs and leaves, have been used to construct buildings and other structures, like bridges. Apart from natur ...

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

Optoelectronic Optoelectronics (or optronics) is the study and application of electronic devices and systems that find, detect and control light, usually considered a sub-field of photonics. In this context, ''light'' often includes invisible forms of radia ...

devices based on organic material, generally named

OLED An organic light-emitting diode (OLED), also known as organic electroluminescent (organic EL) diode, is a type of light-emitting diode (LED) in which the emissive electroluminescent layer is an organic compound film that emits light in respon ...

s, need an encapsulation with low values of WVTR to guarantee the same performances over the lifetime of the device. MVTR generally decreases with increasing thickness of the film/barrier, and increases with increasing temperature.

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. Special care has to be taken in measuring porous substances such as fabrics, as some techniques are not appropriate. For very low levels, many techniques do not have adequate resolution. Numerous

standard Standard may refer to: Symbols * Colours, standards and guidons, kinds of military signs * Standard (emblem), a type of a large symbol or emblem used for identification Norms, conventions or requirements * Standard (metrology), an object ...

methods are described in

ISO The International Organization for Standardization (ISO ; ; ) is an independent, non-governmental, international standard development organization composed of representatives from the national standards organizations of member countries. Me ...

ASTM ASTM International, formerly known as American Society for Testing and Materials, is a standards organization that develops and publishes voluntary consensus technical international standards for a wide range of materials, products, systems and s ...

, BS,

DIN DIN or Din or din may refer to: People and language * Din (name), people with the name * Dīn, an Arabic word with three general senses: judgment, custom, and religion from which the name originates * Dinka language (ISO 639 code: din), spoken ...

etc.—these are quite often industry-specific. Instrument manufacturers are often able to provide test methods developed to fully exploit the specific design which they are selling. The search for the most appropriate instrument is a zealous task which is in itself part of the measurement. The conditions under which the measurement is made has a considerable influence on the result. Both the temperature and humidity gradients across the sample need to be measured, controlled and recorded with the result, and the thickness of the sample should be the same. An MVTR result without specifying these conditions is almost meaningless. Certainly no two results should be compared unless the conditions are known. For example, the effect of temperature on the permeability can be as high as 10% per °C, making it possible that MVTR results achieved at 23°C and 37°C can differ by a factor 4. The most common international unit for the MVTR is g/m²/day, or " metric perm". In the USA, g/100in²/day is also in use, which is 0.064516 (approximately 1/15) of the value of g/m²/day units. 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, barrier testing is conducted on a sheet of material. Calculations based on that can be useful when designing completed structures, clothing, and packages. Seams, creases, access points, and heat seals are critical to end-use performance. For example, the glass of a bottle may have an effective total barrier, but the screw cap closure and the closure liner might not. Performance

verification and validation Verification and validation (also abbreviated as V&V) are independent procedures that are used together for checking that a product, service, or system meets requirements and specification (technical standard), specifications and that it fulf ...

of complete containers, structures, or irregular objects is often recommended. For the special case of

s, where the levels of allowed permeation are in the 10⁻⁶ g/m²/day level, the methods preferred exploit an oxidation of a metal upon the exposure to water.

References

Psychrometrics Packaging Food technology Drug manufacturing Moisture protection Rates

Measurement

See also

Further reading

USP Regulatory Standards

ASTM Standards

References