What is “MVTR”?
MVTR stands for “Moisture Vapor Transmission Rate“, a measure of the passage of gaseous H2O through a barrier. It’s also known as “WVTR“, or “Water Vapor Transmission Rate“.
Most flexible packaging is intended to preserve contents and protect it from the damaging effects of moisture. The amount of protection is indicated in part by the material’s MVTR, which is typically expressed as g/100 in2 /24 hrs. Currently, the best barrier materials on the market today have an MVTR of <.02 g/100 in2 /24 hrs.
How is moisture resistance measured?
Two main testing methods measure MVTR, ASTM E96 and ASTM F1249.
One variation of ASTM E96 uses a special chamber to measure moisture resistance. The chamber 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. 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). This method can be time consuming and pressure changes may impact the actual results.
ASTM F1249 is an MVTR measurement method that uses infrared (IR) detectors to measure changes in RH on the dry side of a film in a chamber similar to the one used in the ASTM E96 method. Water is placed in the bottom to create a 100% RH atmosphere. Barrier material is used to divide the bottom and top. The top side of the chamber is ventilated with dry air and change in RH is measured with an IR detector. One disadvantage of this method is that the RH is limited to 100% unless special equipment is used that allows for control over RH.
At Protective Packaging Corporation, we focus on providing only the highest quality moisture barrier materials. With more than 25 years of experience in the field, we have the expertise to answer any of your questions. More importantly, our experience is what allows us to offer the most effective solutions, no matter the situation.