An article of athletic footwear having an air-filled bladder disposed in a sole structure is disclosed. The air-filled bladder is in fluid communication with ambient air through a filter that permits ambient air to enter the bladder but restricts liquids and particulates from entering the bladder. In operation, the filter and bladder may be portions of a bladder system that absorb shock when the footwear contacts a playing surface. Alternatively, the filter and bladder may be portions of a bladder system that ventilates the interior of the footwear. The filter may be formed of a material such as expanded polytetrafluoroethylene that is attached to a carrier.