Rigid Filters The rigid style filter was developed for variable air volume systems. The filter is available in 6" and 12" depths. The filter media is similar to bag filter media and is separated by either metal, plastic or beverage board stabilizers. Synthetic or fiberglass media is available. The media is enclosed in metal and the filter is available with or without headers. A 24x24x12 filter with a header will typically have 50 sq.ft. of media and an initial resistance of 0.78" w.g. The filter is rated as a UL Class II filter with an operating temperature of 180 degrees Fahrenheit.