The ISO 8787:1986 standard specifies a method for the determination of the capillary absorbent height of paper and Cardboard using the Clem method. This method is suitable for unsizing papers, such as absorbent paper and papers with high Miscellaneous water-absorption, but not for materials with a capillary absorbent height of less than 5 mm within 10 minutes. The test principle is to hang the sample vertically, immerse the lower end in water, and measure the capillary absorbent height after a certain time to evaluate the water-absorption and wetting performance of the paper. This method can provide a scientific basis for the production quality control and application selection of paper.