A muffler of the absorption type for the exhaust gas of an internal combustion engine including a cylindrical porous sound-absorbing body 1, and a film 5 of the metal or other material formed cylindrically on the inner surface of the porous body 1. The film prevents clogging of the pores in the porous...http://www.google.com/patents/US4607721?utm_source=gb-gplus-sharePatent US4607721 - Muffler for exhaust gas from an internal combustion engine
