Abstract: A process is provided for filling a muffler shell with fibrous material. The process comprises the steps of: providing a muffler shell comprising first and second muffler shell outer parts which define an internal cavity when coupled together and an internal structure adapted to extend at least part way through the shell internal cavity for defining at least one channel having one or more openings communicating with the shell internal cavity; placing a form over at least one of the internal structure and the first muffler shell part; drawing a partial vacuum through a first end of the channel; feeding fibrous material into the form while drawing a partial vacuum through the channel; removing the form after the fibrous material feeding step; and positioning the second muffler shell part over at least one of the internal structure and the first muffler shell part.