In this paper, the properties of filtering media used as porous membranes in air cleaners of modern motor vehicles have been analysed. A relation that defines the air filter life has been presented and a dust absorption coefficient of a filtering medium has been defined. Methods of testing filter elements made of nonwoven filter fabrics and working in conditions corresponding to the primary and secondary air filtration stage have been discussed. Results of examining the filtration efficiency, threshold, and restriction characteristics of the filtering media under consideration have been analysed. The dust absorption coefficient km of a nonwoven filter fabric has been determined for the fabric working at different air velocities during the filtration. The impact of the particle size distribution of dust, changed by the intake air pre-treatment in a uniflow cyclone, on the characteristics of the nonwoven fabric under test and on the value of its km coefficient has been examined. The benefits gained from two-stage air filtration have been indicated.