There are many kinds of filter materials, and paper filter materials occupy a large proportion in the filter industry with excellent performance and price ratio. The filter whose filter medium is filter paper is closely related to the performance index of filter paper.

1. Permeability of filter paper
Air permeability is a comprehensive reflection of filter paper performance and is the primary consideration in filter design. It is closely related to the filter's flow resistance characteristics, filtration efficiency, original resistance, ash storage capacity (life) and other performance indicators, the greater the permeability of the filter paper, the smaller the flow resistance, the smaller the original resistance, and vice versa. There is opposite qualitative relationship between permeability and flow resistance.

2. The effect on the filter processing technology
Air permeability is also an indicator of the moisture resistance of filter paper. The larger the permeability of the filter paper, the easier it is to absorb moisture, and the filter paper becomes longer after absorbing moisture. The processing size is not stable, affecting mass production. The processing performance is poor. In severe cases, the quality is degraded. When the end cap is damp before bonding, the filter paper length is 2 ~ 4mm, which affects the height control of the filter element. After bonding, the filter paper is moistened, the filter grain is distorted, and the quality of the filter element is seriously affected.

3. Maximum aperture, average aperture
The maximum aperture and average aperture can be measured using the bubble method, and the maximum aperture is the aperture calculated from the pressure at the first bubble point. The average aperture is the aperture calculated from the bubble point pressure. According to this principle, the maximum and average aperture values of eAO can be taken into account. Bubble point test is used to judge the integrity of the filter. The accuracy of filter can be approximated according to the size of average aperture and maximum aperture. The average aperture is closely related to the filtration efficiency of the filter, and the smaller the average aperture, the higher the filtration efficiency.