Method and system for filling a muffler with fibrous material. The muffler includes a muffler shell comprising a first shell member and a second shell member, at least one partition extending between the first and second shell members, and at least one slot formed in the first shell member above the partition. The first shell member is positioned and held relative to the second shell member to form an open portion, a closed portion, and a space between an upper surface of the partition and the first shell member. Fluid is introduced into the space through a fluid delivery device inserted into the muffler shell through the slot, and fibrous material is introduced into the muffler shell through a filling nozzle inserted into the muffler shell through the open portion. The fluid delivery device and nozzle are removed after filling and the shell members are closed and affixed.