There are two kinds of standards for face mask.

1. New standards 42CFR84 of respiratory protection from dust was published by the National Institute for Occupational Safety and Health (NIOSH) on June 8th,1995 (based on filter category)

N Series: Protection from non-oily suspended particles without time limit

R Series: Protection from non-oily and sweat -oily suspended particles with a time limit of 8 hours
P Series: Protection from non-oily and sweat-oily suspended particles without time limit.
Some particulate matter is oil when attached to static electricity non-woven fabrics. It will reduce static electricity, making small dust penetration, so the anti-oil aerosol filter material should go through a special static electricity treatment in order to achieve the small dust proof.
So every series has classified in three levels: 95%, 99%, 99.97% (that is simply called 95, 99,100), and there is a total of 9 Class filter.

2. The EU EN149 standard

FFP1: Minimum filter effect, "80%

FFP2: Minimum filter effect, "94%

FFP3: Minimum filter effect, "97%

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