A filter cartridge (5), suitable for attachment to a respiratory mask, has a housing that includes an air inlet (27), an air outlet (39), and filter material (17, 19) through which air to be filtered travels through when passing from the inlet to the outlet. At least part of the housing includes a sheet...http://www.google.com/patents/US20040055604?utm_source=gb-gplus-sharePatent US20040055604 - Filter element that has a thermo-formed housing around filter material
