DIFFERENCE BETWEEN N95 AND R95 RESPIRATORS
The difference between the two pertains to their resistance to oil-based particles.
3M puts it like this, “Under the NIOSH classification system, ‘N’ rated respirators can only be used for particles that do not contain oils. But, ‘R’ rated respirators may be used in environments that contain oily particles.”
Officially, NIOSH has two designations for oily-based particle disposable respirators – R95 and P95. The “R” rating is said to be “somewhat resistant to oil”. The “P” rating is said to be “strongly resistant to oil”.
In other words, the R95 has an 8 hour service life. The P95 has a 40 hour or 30 day service life (whichever comes first). You can read more about this in the following NIOSH article: NIOSH-Approved Particulate Filtering Facepiece Respirators.