A filter assembly for an enclosure, particularly for an ostomy bag, is described having an enclosure side, a first layer which is gas permeable, and an adsorbent layer comprising adsorbent particles dispersed in a fine fiber web. The enclosure side of the filter assembly includes an adhesive zone in which adhesive is present having an outer adhesive perimeter and a weld area surrounding at least a portion of the adhesive zone, where the filter assembly is heat-sealable to the enclosure at the weld area. A method of assembly is also described.