water vapor transmission rate tester adopts the principle of infrared method. Fix the pre-treated sample in the middle of the test chamber, divide the test chamber into a high-humidity side and a low-humidity side, the humidified nitrogen flows on one side of the film, and the dry nitrogen (carrier gas) flows at a fixed flow rate on the other side, in the presence of a humidity gradient, water vapor will permeate from the high-humidity side to the low-humidity side, and the water vapor that passes through the sample is carried to the infrared sensor by the flowing dry nitrogen, and  the water vapor transmission rate (and other parameters) of the sample is obtained by the electrical signal output by the sensor.