Water vapor permeability is a measure of the passage of water vapor through a material. It is also known as water vapor transmission rate (WVTR) or moisture vapor transmission rate (MVTR).
It is the mass of water vapor that is transmitted through a measured area in a specific unit of time under specified conditions of temperature and humidity.
Package materials testing, as well as package evaluation and testing, are important parts of the research and development process. Testing helps ensure that new primary packaging materials and package designs are created specifically to handle real-world situations.
This specifies an instrumental method for determining the water vapour transmission rate of plastic film, plastic sheeting and multi-layer structures including plastics, using a humidity detection sensor. This method provides rapid measurement over a wide range of water vapour transmission rates.
This test method covers dynamic evaluation of the rate of transfer of water vapor through a flexible barrier material and allows conversion to the generally recognized units of water vapor transmission (WVT). This test method is limited to flexible barrier sheet materials composed of either completely hydrophobic materials, or combinations of hydrophobic and hydrophilic materials having at least one surface that is hydrophobic.
This method describes a procedure using a closed cell to evaluate rapidly, at any normal or elevated temperature, the water vapor transfer rate (WVTR) of packaging materials in sheet form, especially barrier films of coated paper. This procedure involves clamping a specimen sheet between a high-humidity chamber (90% RH) and a dry chamber (5% or less RH) and determining the rate of change of humidity in the dry chamber. By means of a calibration curve these dynamic test results can be converted to grams of moisture per square meter-day.