A HEPA filter is defined by its effectiveness at removing airborne contaminants from the air stream. EN1822:2019 is a factory test that helps to guarantee that the filter meets the removal efficiency needed. During factory tests of the HEPA filter, a test aerosol is used to measure the levels of airborne particulates that bypass the filter. Each HEPA filter is measured against the MPPS (most penetrating particle size) to ensure its effectiveness against even the smallest airborne contaminants. The MPPS of a filter ranges from 0.1 to- 0.2 microns. This means that when a HEPA filter is rated H14, it is 99.995% effective against the MPPS. When measured against other particulate ranges, it is often much more effective. At Camfil, we scan-test 100% of our HEPA filters utilising our lab capabilities.