A face mask comprising an elongated sheet of porous material having upper and lower longitudinal edges and transverse side edges. A line of stitches of elastic material is sewn to the material along both its side edges, and a length of elastic cord at each side edge is secured to the material by interweaving...http://www.google.com.hk/patents/US4014047?utm_source=gb-gplus-share專利 US4014047 - Face mask
