Why measure efficiency at 0.3 micron?
Media air cleaners are rated accordingly to their ability to capture particles 0.3 microns in size. Why? Because these particles are the most difficult to remove from the air. In standard tests using dioctyl phthalate (D.O.P.) which generates 0.3 micron particles when tested, Honeywell hospital grade filters were rated at 95% efficiency and HEPA filters at 99.97% efficiency. But these are minimum ratings. The laws of physics make Honeywell air filters actually more efficient on particles smaller or larger than 0.3 microns. And these high efficiencies are maintained over the life of the filter.
