HEPA stands for high efficiency particulate air. Essentially, it means you can clean the air as you clean your floors and upholstery. A lot of older vacuums kick up more dust than they clean. HEPA filters are designed to trap very small particles, picking up pollutants, dust, and allergens that would normally remain in the air. It is even thought that HEPA filter vacuums can reduce the level of PBDEs (harmful compounds found in many everyday household products) in a home.
A trademarked HEPA filter removes at least 99.97% of particles such as dust, animal dander, smoke, lead, mold and other allergens. It is important to make the distinction between true HEPA filters and "HEPA-type" or "high-efficiency" filters, which are widely advertised, but can actually be up to 55 percent lower in efficiency than true HEPA filters.
True or absolute HEPA filters must be able to trap at least 99.97% of particles of .3 microns to earn the HEPA label. True HEPA filters will have a serial number attesting to such a performance level. If you are in the market for a HEPA filter vacuum, check the label for a serial number and air cleaning test results before you buy.
HEPA-type or HEPA-like filters may closely resemble true HEPA filters, but they do not have to meet the same standards as true HEPA filters. These vacuums tend to cost less, but they are not as effective at cleaning the air as true HEPA filter vacuums.
A true HEPA filter vacuum is another great tool to have in your green cleaning arsenal.