A filter material for an air filter may include a substrate layer on an inflow side and a fine-fiber layer on an outflow side relative to a flow direction. The filter material may include a connection region arranged between the substrate layer and the fine-fiber layer. The substrate layer, connection region and fine-fiber layer may include pores having an aggregate degressive pore size with respect to the flow direction. A combined thickness of the substrate layer, connection region and fine-fiber layer may be at least 0.35 mm. The substrate layer may include a cellulose material and have an impregnation of resin disposed along the inflow side. The resin may amount to approximately 22% by mass of the substrate layer.

A filter holding device includes an opening portion and a filter. The opening portion communicates between an inside and an outside of the filter holding device. The filter is disposed in the opening portion and includes a first side and a second side. The first side is located adjacent to the inside of the filter holding device. The second side is located adjacent to the outside of the filter holding device. The filter has a larger weight density per unit volume at the second side than a weight density per unit volume at the first side and has a larger area of a surface intersecting a communication direction at the second side than an area of a surface intersecting the communication direction at the first side.