What exactly is a HEPA filter?

The HEPA (High Efficiency Particle Arresting) filter was developed by the U.S. Atomic Energy Commission to filter out sub-micron particles.  All true medical grade HEPA is laser-tested and must remove a minimum of 99.97% of all particulate matter greater in size 0.3 microns.  Austin Air’s HEPA filters also remove 95% of all particles larger than 0.1 microns.   All Austin Air purifiers feature true medical grade HEPA filters.