Merv is not a brand of filter; instead, it is the name of a rating system that describes the efficiency of the air filter, and the higher the rating defines whether or not the filter is good for its application. The ratings are available from 6 to 13.
Merv 6 filters are used for basic filtering purposes, which work well to remove larger particles of dirt or lint. Merv 11 are produced for those who suffer asthma as they increase the filtering ability of dust particles up to 65 percent, versus standard fiberglass filters. Merv 13 filters offer the best filtering capabilities and remove up to 90 percent of dust particles.