PERMATRAN-W® 3/31 3/31 is a water vapor transmission rate (WVTR) testing system designed to assess barrier materials used in packaging applications. By testing barrier materials for WVTR under a range of conditions, these systems enable you to select the best packaging material, at the best cost. This data assures you product shelf-life and certain packaging characteristics will be met when introduced to the market. The 3/31 features a series of technological enhancements over prior models. It is faster and more stable, with increased upper and lower ranges, and 100 times greater sensitivity. These high sensitivity systems perform tests directly at the materials "real world" temperature and relative humidity. (There is no need for salt solutions to select humidity.) Modular hardware, flexible test cell configurations, and improved easy-to-use software make your barrier testing application simple, accurate, and free of subjective decisions.