an air filter for a combustion engine for off - load motorcycles is made from a porous foam material . the air filter has contiguous side surface forming a cavity with at least two openings where the side surface contains at least one filter layer , a bottom surface closing at least one of the two openings where the bottom surface contains at least one filter layer , where the side surface has more air resistant than the bottom surface . the side surface has more air resistant than said bottom surface by arranging any combination of thickness of the surfaces , number of layers , and porosity ratio of the layers .