Very frequently filter elements made from pleated filter media are used to solve gas purification problems. It is necessary to develop models that relate the filtration performances of a plane medium to the filtration performances of the pleated medium and the ones of the whole filter element. The knowledge of the relations between pleat geometry and filtration performance will allow an optimized design of the dimensions of the pleats. Optimization criterion is the minimization of the pressure drop for a given particle penetration probability of the filter element. Based on approximation solutions of the Navier-Stokes equation, a model for the overall pressure drop of a filter element is developed. Furthermore, equations for the overall particle penetration are given. Afterwards the general models are simplified. The calculation results are compared with data from the literature and the authors’ own experimental results.