The filters applied in air handling units extend their life period by ensuring the protection of air handling units against pollutants, which can cause their faulty operation or damage. Depending on their class, filters can be applied as terminal filters in ventilation and AC installations in rooms with medium air purity requirements (G4, F5 filters), or as pre-filters (preceding higher-efficiency filters) in rooms with high air purity requirements (F7 and F9 class filters).