Why is the testing done with a 0.3-micron particle size test aerosol?
Filter efficiency studies have shown that 0.3-microns is the “Most Penetrating Particle Size (MPPS)” for HEPA filter media. Efficiency is typically greater than 99.97% against larger or smaller particle sizes. Particles larger than 0.3 microns are typically more easily trapped, or intercepted, by the media. Smaller particles often lack sufficient mass to penetrate the media.
