What is PM2.5 BFE? July 14, 2020 23:48 Updated BFE stands for Bacterial Filtration Efficiency — meaning it can filter PM (particulate matter) of 2.5 microns! Related articles Do you need to replace the filters? Is the FIONx Protective Mask an N95? How many washes does this last? Does this mask have a nose guard? What way should the filter face?