This specification covers throw-away, flat panel-type filter units for use in air conditioning, heating, and ventilating systems. This specification also includes panel-type filters with pleated media. The filters are furnished in two types as follows: type I - throw-away frames and media, and type II - permanent frames with replaceable media. The filters are furnished in three grades as follows: grade A - standard dust-holding capacity, grade B - high dust-holding capacity, and grade C - high resistance. The adhesive oil, filter initial resistance, filter average arrestance, and filter dust holding capacity conform to the requirements specified.