The ASTM F1249-20 standard provides a test method for the determination of water vapor transmittance (WVTR) of Plastic films and sheets by modulated infrared Sensors. This method is suitable for plastic sheets and films with a thickness of not more than 3 mm, including synthetic and natural polymers, and their coating materials. WVTR is a key indicator for evaluating the performance of Encasement materials and is closely related to product shelf life and Stability. This method provides an accurate WVTR value, which is suitable for determining the validity of Encasement materials and can be used as a referee test method in buyer-seller agreements. Users should establish appropriate safety specifications according to actual needs and comply with relevant regulations.