Abstract: The disclosure embraces a method of processing thin-walled tubular metal members for providing louvered openings therein, the tubes being of a character utilized as gas passage and sound attenuating means in muffler constructions for use with internal combustion engines, the method embracing shearing or lancing openings in the tube wall by employing shearing forces directed radially inwardly of a tubular member for forming the openings and deflecting inwardly the adjacent sheared or lanced portions providing inwardly deflected louvers for the openings, the method preferably including the method step of deflecting portions of the wall of the tube adjacent the openings outwardly in forming louvered openings.