Fibrous filters exhibit efficiency decreases with time when they are used to control metalworking fluid mists. These efficiency reductions, which are related to the amount of liquid coalesced within the filters, may lead to unacceptable increases in worker exposure to potentially hazardous droplets. Researchers have developed equations to predict changes in efficiency and pressure drop as filters collect and retain droplets. These expressions can be used to model wetted filter performance from when a filter is new until it reaches a steady operating condition. However, the equations do not account for the influence of filter thickness or fiber material on filter performance. Because filter thickness and fiber material may affect the amount of liquid present within filters, control equipment manufacturers need to understand the influence of these factors on filter performance to design better filters for mist control. The proposed research has four parts: (a) Design an improved test apparatus for measuring the performance of custom-made test filters; (b) Conduct experiments to evaluate the influence of filter thickness and height on filter performance; Conduct experiments to evaluate the influence of fiber material on filter performance; (d) Utilize the data collected from experiments to modify the numerical model used to predict wetted filter performance. With the updated model, design a filter that minimizes efficiency reductions and pressure drop increases over the life of the filter. When the proposed research is complete, a comprehensive numerical model of the performance of wetted filters will be available to manufacturers of filter media and control equipment. Using the model, manufacturers will be able to design filters that protect workers more effectively from exposure to potentially harmful metalworking fluid mists. Other types of filters that may be designed better using the improved model include respirator filters, mist eliminators in chemical plants, and high efficiency filters used to prevent the release of radioactive droplets in case of a nuclear reactor accident.