Moisture Vapor Transmission Rate Water Vapor Transmission Rate, (also known as WVTR water vapor transmission rate), which moisture vapor can permeate through the structure and into a dry atmosphere on the other side. It is recorded in units of gm/100 inches square/24 hour (g/m2/24hr). WVTR is dependant on the gauge of the structure, the materials used in the structure, and the quality of the materials used. Vapor can pass through channels in the seals, holes, tears, or imperfections in the package.