GermGuardian FLT4825 True HEPA GENUINE Replacement Filter B is a combination filter. It includes a True HEPA filter that captures 99.97% of allergens as small as .3 microns. It also contains a pre-filter/activated carbon filter that captures odors from cooking, pets and smoking. It is recommeded to use with with GermGuardian AC4900, AC4825, AC4850PT, PureGuardian AP2200CA and Black+Decker Model BXAP148. The use of this genuine Guardian Technologies replacement part will maintain the product's performance and warranty.