A filter has first and second filter media (2, 3). The filter media define a flow space (4) between them receiving a device (5) for separation and flow guidance and dividing the flow space such that a functional space (25, 26) is disposed adjacent to the first or the second filter medium. The first filter medium (2) defines a hollow space (21) toward the outside, and the second filter medium (3) defines a hollow space (22) toward the inside. Each of the hollow spaces (21, 22) can be connected to at least one fluid duct (23, 24). The flow space (4) including the two functional spaces (25, 26) can be connected to at least one further fluid duct (27) that is separated in a fluid-tight manner from the other fluid ducts (23, 24).