The set includes 2 high-quality G4 class filters. ISO16890 Classification Coarse 75% G4 filters are used to protect the ventilation unit and ventilation system from contamination caused by larger particles such as dust, bugs and lint. They trap some of the larger pollen, but do not provide complete protection against all types of pollen. The main advantages of G4 filters are the low resistance and attractive price. G4 filters last longer than M5-F9 filters and result in lower energy consumption and lower noise emissions during operation.