A multi-layer filter 20 for location over an aperture or vent 15 provided in the wall of an ostomy product, namely a bag. The filter comprises a hydrophobic layer 21, preferably formed from Polytetrafluoroethylene (PTFE), which is positioned directly adjacent the vent and/or wall when the filter is attached to the ostomy product. In one arrangement (Fig 2) a first side of the hydrophobic layer is connected directly to the wall, with this connection holding the filter to the wall. A de-odorizing layer 22, preferably formed from a carbon-based material, may be positioned adjacent the hydrophobic layer, with a gas and liquid impermeable layer 23 placed adjacent the de-odorizing layer.
