What is “MVTR”?
MVTR stands for “Moisture Vapor Transmission Rate“, a measure of the passage of gaseous H2O through a barrier. It’s also know as “WVTR“, or “Water Vapor Transmission Rate“.
How is moisture resistance measured?
Moisture resistance is measured in a special chamber where it is divided vertically by the substrate/barrier material. A dry atmosphere is in one chamber, and a moist atmosphere is in the other. A 24-hour test is run to see how much moisture passes through the substrate/barrier from the “wet” chamber to the “dry” chamber. Standard test procedures (TAPPI T-464, ASTM E96) can specify any one of five combinations of temperature and humidity in the “wet” chamber. The toughest conditions are 100°F / 95%RH (Relative Humidity). Currently, the best barrier materials on the market today have an MVTR of <.02 g/100in2/24hrs.