The rigid particles that can form a porous cake layer make the filter cake have good permeability and low fluid resistance. It has chemical stability. Incompressibility within the operating pressure range. In the paper industry, filter aids are chemicals added to improve the water repellency and dehydration rate of wet paper from the papermaking web. Generally, it is a cationic polymer polyelectrolyte, such as polyethylene imide, cationic starch, polyamide, polyacrylamide, etc.

Substances that can improve the filtration efficiency of the filtrate. Insoluble inert materials with different degrees of fineness are used to prevent excessive compaction of filter residue and smooth filtration. In filtration operations, an auxiliary powdery substance added to reduce filtration resistance, increase filtration rate, or obtain highly clarified filtrate is called a filter aid.