N series: no time limit for protection of non-oily suspended particles
R series: Protection against non-oily suspended particles and sweat-oily suspended particles for eight hours
P series: protection of non-oily suspended particles and sweat oily suspended particles without time limit
When the carrier of some particulate matter is oily, and these substances attached to the electrostatic non-woven fabric will reduce the electrical properties and allow the fine dust to penetrate. Therefore, the anti-aerosol-containing filter material must undergo special electrostatic treatment to prevent fineness. The purpose of dust. So each series is divided into 3 levels: 95%, 99%, 99.97% (referred to as 95, 99, 100 for short), so there are 9 sub-categories of filter media.