HEPA filter has to meet a strict test to be called labeled HEPA. It needs to capture almost all of those 0.3 micron particles in one go."}" data-sheets-userformat="{"2":513,"3":{"1":0},"12":0}">Basically, a HEPA filter has to meet a strict test to be called labeled HEPA. It needs to capture almost all of those 0.3 micron particles in one go.