The TAPPI T 538 standard specifies a method for measuring paper and Cardboard asperity using the Sheffield method. This method quantifies asperity by measuring paper surface air flow resistance and is suitable for all types of paper and Cardboard. During the test, the specimen is sandwiched between two parallel plates, the air passes through the surface of the specimen under a specific pressure, and the instrument records the air Flow rate to calculate the asperity value. This standard provides a unified quantitative basis for the evaluation of paper and Cardboard surface characteristics. It is widely used in the fields of quality control, product development and performance evaluation to help ensure the performance conformity of paper and Cardboard in printing, writing, Encasement and other applications.