eXtra - Protective Face Mask - Replacement Filters - 1 3-Fliter Pack(s) - NPN: 00000000 -- PM2.5 Filter Included with Mask2.5 microns is pretty darn small less than a third of a human hair! The included PM2.5 filter can handle particles that tiny. Even with daily use, the filters are effective in filtering out PM 2.5 for up to a week thanks to the multi-layered non-woven fabric construction and activated carbon layer.Meltblown Triple Filter LayerMelt blowing is a conventional way of making micro- and nanofibers. Unlike traditionally woven fibers, the melt blowing process weaves an intricate web for filtering gas and air.Activated Carbon LayerActivated carbon is an incredibly porous surface that is used in gas filtration to trap oil vapors, odors, and other hydrocarbons from the air.Non-Woven FabricNonwoven fabrics provide a myriad of specific functions including filtration, use as a bacterial barrier, and sterility. This is why non-woven fabrics are commonly found in hospital-grade materials.