The article describes a methodology for determination of permeability and inertial resistance coefficient of filter inserts used for the separation of solid and liquid impurities in natural gas. The parameters of the filter inserts are described by analytical relations and their real values are obtained experimentally. The realized experiment was focused on the measurement of the pressure drop in the insert, with which both permeability and inertial resistance coefficient were possible to be expressed. The experiment was performed on the reduced physical model of the filter separator, which was constructed at a scale of 1:127. During the experimental measuring the working medium was pressure air. In a real filter separator there is compressed natural gas used as the working medium. The reduced model, therefore, had to meet the basic requirement of similarity of flowing in the model and the real object, which was based on equality of the Reynolds criteria for the work and the model.