A respirator face mask formed from a silicone or other vulcanized rubber with a multi-compound curved face seal having a superior configuration for facial fit. The mask is held by four support buttons and two straps attached thereto having a reverse leverage pulldown effect to pull the mask into contact...http://www.google.es/patents/US4414973?utm_source=gb-gplus-sharePatente US4414973 - Respirator face mask
