A filter assembly includes a casing having of a polymeric film and bounding a compartment, the casing having an inlet opening communicating with the compartment and a first outlet opening communicating with the compartment. A first filter includes a porous filter body through which gas can pass and has a pore size smaller than 1 μm, the first filter being coupled with the casing so that the filter body is at least partially disposed within compartment of the casing and so that gas passing through the compartment of the casing from the inlet opening to the first outlet opening must pass through the filter body.