A method for containing fibrous material within muffler comprises the initial step of providing an internal assembly of a muffler. In the next method step, a sheet is placed about the internal assembly to form an enclosure about a compartment. In the next method step, the compartment is filled with a fibrous material. A muffler according to the invention comprises a muffler having an outer shell having an internal cavity and outer edges. An internal assembly is inserted within the internal cavity. The internal assembly comprises partitions and a sheet about the internal assembly and extending between the partitions from an enclosure between the partitions. The enclosure is filled with fibrous material. End plates are joined to the outer edges of the outer shell.