A filtering face mask that has a mask body and an exhalation valve. The mask body is adapted to fit over the nose and mouth of a wearer. The exhalation valve is positioned on the mask body substantially opposite to a wearer's mouth. The exhalation valve comprises a valve seat that has a seal surface,...http://www.google.es/patents/US7428903?utm_source=gb-gplus-sharePatente US7428903 - Fibrous filtration face mask having a new unidirectional fluid valve
Fibrous filtration face mask having a new unidirectional fluid valve
