what is mpr rating
3M describes Microparticle Performance Rating (MPR) as The 3M MPR (Microparticle Performance Rating) focuses on a filter's ability to capture smaller particles between 0.3 and 1 micron in size.
Based on independent laboratory tests, 3M s MPR measures a filter s ability to capture submicron particles that make up 99% of the particles in the air, such as bacteria, smoke and smog. The MPR can be used to compare filters, however MPR cannot predict how a filter will actually perform in your home.