HEPA

High Efficiency Particulate Air. The US Department of Energy standard requires 99.97% capture of particles 0.3 microns or larger.

The 0.3 micron threshold is the most-penetrating particle size; smaller and larger particles are captured at higher rates. True HEPA requires a sealed airflow path in the vacuum body; a HEPA filter in a leaky body does not deliver HEPA performance.