In simple terms, it is easier to understand NIOSH ratings if you look at them like this. Respirators with "N" in their classification are NOT resistant to oil or oil based particles. Respirators with the "R" classification are somewhat resistant, and those with a "P" are considered highly efficient at filtering out oil or oil based particles. The second part of NIOSH classification is a number.  For most of us, a N95 respirator will effectively filter harmful particles that could cause allergic or asthmatic reactions. The "95" means that 95% of the "most penetrating" particles (generally, .03 microns or greater in size) are effectively captured and filtered by these masks. A "100" rating would mean that 99.7% of these size particles are effectively filtered. This is also considered HEPA filtration or HEPA equivalent.

You may have noticed the Respro masks do not have a NIOSH rating. These masks are manufactured in the UK and do not fall under the NIOSH classification. However, they do have to meet similar European filtration standards. The European Standard EN149 FFP1 is the U.S. equivalent of the N95 NIOSH rating. The Respro Techno Mask features a filter that meets the EN149 FFP1 filtration standard. So, with these masks you can receive the same filtration as you would find with N95 respirator or mask.