This air filter / grease filter is made of multiple layers of both flat and corrugated expanded aluminum and is enclosed in alight duty aluminum frame. The expanded metal layers in this air filter / grease filter are of differing weights and diamond sizes and some are flat expanded metal and some are corrugated expanded metal making it more efficient than other expanded metal filters. A Good Filter Company Innovation. This inconsistency in the filtering media makes this air filter / grease filter more efficient because the air must take a meandering pathway through the filter and also makes this filter stronger and more durable. Another Good Filter Company filtering enhancement. The frame is aluminum and is closed on one corner with an aluminum rivet on a flattened surface for more solid holding power. This air filter / grease filter is made in the standard Good Filter Company tradition of hand closing the frame and hammering all corners for smoothness. Our unique construction methods make this a better quality, more efficient economy duty expanded metal air filter / grease filter. This air filter / grease filter will perform well in light to medium duty usage for a longer period than other expanded metal filters of this thickness. It is an excellent air filter for HVAC make up air applications.