They filter to .03 micron. The filter can act as a breeding ground for bacteria, mold and fungus. They do not remove odors, gases, pesticides, viruses, and many bacteria. They reduce airflow due to the tight pores of the filter. They are generally not used in central systems, and sold as stand-alone units only.
Carbon filters consist of carbon impregnated filter fabric or granulated carbon.
These filters usually have a foam or fabric filter to hold the media. Carbon has the unique capability of acting as a physical filter trapping particulate, and on a chemical basis by reacting with some odors and some of the heavy gases. They reduce airflow. Fiber or open-cell foam filters rely on the air passing through a matrix of foam cells or fibers of fiberglass, wire, plastic or cloth. Typically, these filters only stop medium to large particulate.