I know I'm going to sound like a shilling Eufy OEM but seriously if you have a Eufy 11S Max you need to use these filters and not a third party filter. I have tried third party filters and they are cheaper because they do not filter small particles as well. I know this objectively because I use the blower every day to clean the filters after starting Eufy (to extend filter life and reduce overall costs) and I can see the dust the blower blows through the cheaper filters blow (in the suction direction), and Eufy brand filters don't have this problem.