Polytetrafluoroethylene (PTFE) film surface is smooth and resistant to chemicals, which cover a variety of needle felt close to the surface, and has played a role in a disposable dust layer, all the dust trapped in the surface of the film to achieve surface filtration; Although initial resistance but because the larger pore size is extremely small (<0..2um) can effectively control the speed of content gathering dust, avoid rapidly rising early resistance, and because the film surface smooth, with excellent chemical stability, aging, and water-repellent