Take out the felt from the water before use and squeeze out the water to make the weight of the felt about 1g. This standard is revised as: remove the felt from water before use. Place it in the middle of four absorbent filter papers (two at the top and two at the bottom, and the test surface is in horizontal contact with the pool paper), and then place a weight of (9001 + - 10) g on the filter paper for 1 min to squeeze out the water, so that the weight of the felt reaches about Ig. It is verified by experiment. The added content can meet the requirements of iso11640, at the same time, the tester can adopt a unified test method and operate more accurately. Reduce the error of the test and ensure the consistency of the test results.