A method for forming odd-shaped mufflers is achieved by first introducing an unfilled muffler insert having a desired number of pipes and partitions within a two-piece shaped tool. Fibrous material is introduced within desired compartments formed between the shaped tool and unfilled insert to form a filled insert. The shaped tool and filled insert are then placed on a winding device. A yarn thread is then wound and secured around the fibrous material within a gap created between the two pieces of the shaped tool. The winding device and shaped tool are then removed from the filled and wound muffler insert. The wound and filled muffler insert may then either be pressed into a previously formed muffler shell, or alternatively, the muffler shell may be formed around the wound and filled muffler insert to form the muffler.