Compatible with Honeywell 10500 and 17000 air cleaners, the Honeywell True HEPA filter is up to 99.97 percent effective at removing particles as small as .3 microns from the air. True HEPA filters collect such annoyances as dust, mold spores, mites, pet dander, and other troublesome allergens. The difference between a HEPA filter and an ionizer is that the former collects and removes the harmful particles from the air, whereas the latter merely displaces it and pushes it around the room. Overall particle reduction depends on many factors, including the amount of air processed, the pollutant type, and the pollutant's introduction rate in the environment.