The Revolutionary New 3Mâ„¢ High Air Flow (HAF) Filtration Media reduces your risk of pressure drop. HAF uses microstructure technology to create an array of air flow channels. These channels are electrostatically charged to attract and trap oppositely charged, unwanted particles along the air channel walls, while leaving the channel open for air flow. The electrostatic charge greatly increases HAF’s ability to capture and retain smaller and intermediate sized particles, without an increase in fiber density. Once the particles have made contact with the filter media, they are held by intermolecular attractive forces better known as van der Waals forces. Electrostatically charged 20 mm HAF media captures particles as small as 6.5 microns with 74% fractional efficiency in low flow rates of 20 ft./minute. (As reference, the diameter of a human hair is about 100 microns and the human eye typically can not see particles less than 50-60 microns). HAF allows significantly more air to flow over your coils or through your fans than typical loaded filters. HAF is not HEPA rated, it is not considered an extremely high efficiency media or suitable as a primary furnace filter. However, it is often used as a secondary pre-filter in these applications. As a pre-filter, HAF captures particles in front of expensive or hard to replace high efficiency filters. It can increase efficiency and extend service life, without signicicantly restricting air flow. No matter what the application, HAF users operate cleaner, better performing systems with longer and less expensive maintenance cycles.