The TAPPI T 536 standard specifies a method for measuring the air passage resistance of paper using the high voltage Gurley method. Air passage resistance refers to the ability of paper to hinder the flow of air and is an important parameter for evaluating the compactness and breathability performance of paper. The standard describes in detail the use of test equipment (high voltage Gurley instrument), sample preparation, test conditions and operation steps to ensure the accuracy and conformity of the measurement results. Through this method, the air resistance of paper can be quantified, providing an important reference for the application of paper in the fields of Encasement, filtrate, etc. The standard is applicable to all kinds of paper, especially for paper materials with high density or low air permeability.