A trademarked HEPA filter removes at least 99.97% of particles such as dust, animal dander, smoke, lead, mold and other allergens. True or absolute HEPA filters must be able to trap at least 99.97% of particles of .3 microns to earn the HEPA label and will have a serial number attesting to such a performance level. When selecting a HEPA filter vacuum, check the label for a serial number and air cleaning test results before you buy. "HEPA-type" or "high-efficiency" filters are widely advertised and usually cost less, but can be up to 55% lower in efficiency than true HEPA filters.
A true HEPA filter vacuum is another great tool to have in your green cleaning arsenal.