HEPA is an acronym for “High Efficiency Particulate Air”. This term is officially defined by the United States Department of Energy. A HEPA filter can remove at least 99.97% of particles with a size of 0.3 microns. This diameter specification of 0.3 microns is used because it is the worst case scenario for HEPA filters. This 0.3 micron size particle is known as the Most Penetrating Particle Size (MPPS). This means that particles which are larger or smaller are trapped with HIGHER efficiency than particles which are 0.3 microns in diameter. Testing has shown that particles larger than 0.3 microns are more efficiently trapped because of their larger size AND particles smaller than 0.3 microns are more efficiently trapped because they lack the mass to penetrate the filter. Therefore, HEPA filters are certified using the worst case particle size which results in the worst case efficiency rating (i.e. HEPA 14 filters out 99.995% or BETTER for all other particle sizes, and at least 99.995% of particles 0.3 microns).
 
Please note there is a 7 day lead time, often goods are delivered much sooner