The air filters of the internal combustion engines, being a cheap component, usually, are replaced before they reach their complete filtering capacity. This problem is mainly for the motor vehicles that are used in normal conditions of use. When the vehicles are used in special conditions, like in constructions, agriculture or on unimproved roads, the dust contamination is a severe one in a short amount of time. For those extreme conditions, the motor vehicle manufacturers specify a replacement period, smaller than the normal one. Another specification can be the one that suggests to blow the dust regularly, from the filters. In those conditions the authors tested on a test bench different filters filled with different quantities contaminants (dust). The testing bench has an absolute filter that captures the dust particles that passes through the tested ones. After that the tested filter will be blow off with compressed air and retested. For both cases the absolute filters will be analyzed. The impurities are usually minerals with irregular sharp corners. Blowing them, the particles will travel in the opposite direction, from inside to outside of the filtering material. This way the filtering material will be damaged and will make possible of passing high quantity of dust, including bigger higher particles. The paper will show, with obvious results, the necessity of avoiding of reusing air filters that were blown with compressed air.