High Efficiency Particulate Arresting (HEPA)  filters are the most efficient filter at trapping very small particles, including the following: mold spores, many bacteria and viruses, and, of course, larger items such as dust.

HEPA Air filters are an effective way to enhance the quality of air in your home.

The American Society of Heating Refrigeration and Air Conditioning Engineers (ASHRAE)and the air filter industry have come up with a standardized rating system - the MERV rating.  This numbering system makes it easier to evaluate and compare mechanical air filters.