According to the Environmental Protection Agency (EPA), indoor air can be 2-5 times more polluted than the air outdoors. HVAC Filters are composed of highly porous beds of glass or plastic fibers. The fibers collect airborne dust and particles and they are responsible for cleaning the air in air conditioning systems. Most HVAC filters are single-use, disposable items although there are a wide array of filters that can improve the air quality in your home. Before we discuss the types of filters, it is important to understand the basis for comparison. Recently the American Society of Heating Refrigeration and Air Conditioning Engineers (ASHRAE) and the air filter industry have come up with a standardized rating system of a MERV rating for each type of air filter.