Expanded Metal filters are constructed of individual layers of expanded metal and assembled in a crisscross pattern. The expansion openings are diamond shaped and each subsequent layer has the diamonds placed in the opposite direction as the previous layer for more efficiency at capturing particulates. There is also at least 1 layer of screen wire in the center of the filter. Depending upon the thickness of the filter, some of the expanded metal layers are corrugated or flattened in order to completely fill the frame of the filter.
These filters have various uses including as barrier filters for insects, rodents and larger particulates. Air resistance is less than metal mesh filters but so is efficiency. They are however, almost indestructible and very easy to clean. Used mostly for capturing larger particulates in industrial and commercial applications. Standard duty expanded metal filters are made of Aluminum.