The higher the MERV value, the more efficient the air filter is at removing particles. At the lower end of the efficiency spectrum a fiberglass panel filter may achieve MERV 4 or 5. At the higher end, filters that achieve MERV 13 or 14 are typically used in hospitals and clean rooms. High MERV filters are capable of removing higher quantities of extremely small contaminant (particles as small as 1/300 the diameter of a human hair). Higher MERV ratings can create problems with greater airflow resistance. This is also referred to as static pressure. With most filters the filter media becomes denser, and static pressure increase, as the filter efficiency increases. Increased static pressure forces the system fan motor to work harder as it pushes air through the filter. This also increases energy consumption. So for optimum performance, consumers should select the highest efficiency filter with the lowest static pressure.