The ASTM F3299-18 (2023) standard specifies a method for the determination of water vapor transmittance (WVTR) of Plastic films and sheets using electrolysis detection Sensors (Coulometry P2Ø 5 Sensors). This method is suitable for flexible barrier materials composed of single or multi-layer synthetic, natural polymers and foils. WVTR is a key indicator for evaluating the performance of Encasement materials, which directly affects the shelf life and Stability of products. The standard provides a reliable WVTR Measuring method for scenarios where accurate water vapor transmittance data is required. If the buyer and seller agree on the test procedures and conditions, this method can be used as a referee test method.