Air filter media are used in HVAC and typically comes in rolls. These media are sized, cut and inserted into frames to filter particulate such as dust, pollen, mold, and perhaps some bacteria, from the air in a building. Filter media are typically made of fibrous or porous polyester, foam or fiberglass. Of particular importance in differentiating filter media is its MERV rating. Minimum Efficiency Reporting Value (MERV) is a standard that rates the overall effectiveness of air filters. The higher the MERV, the finer the filtration. For more on HVAC system air filters for buildings, see our flat air filters, pleated air filters, pocket air filters, and HEPA air filters.