-Replaceable PM2.5 Filter -Provides 5 extra layers of filtering protection in addition to cotton mask -Not washable or resuable -Recommended to use with the cotton face mask  -Keep a layer of face mask fabric between filter and your mouth (Use with face masks that have an open slit in mask that allows filter to be slid inside) -Recommended lifespan of 3-4 days (Replace every 3-4 days) -Packaged in pack of 10 pcs