Liquid aerosols produced in many manufacturing and refining processes need to be filtered from the exhaust streams. Where wettable fibers are used in the filters, the aerosol liquid collects on the fibers. Observation shows that thin films develop on the fibers, and the liquid drains down the fibers under the action of gravity. A model is developed for the flow of liquid in these films, and careful experimentation confirms the nature and importance of the flow pattern. The resultant overall efficiencies of the filter are also calculated from a theoretical analysis and compared with the results of experimentation using counting techniques. The theoretical and experimental results agree excellently for the range of aerosol sizes that are detectable by laser diffraction and cascade impactor techniques.