Abstract: This invention provides preforms of continuous glass fiber strands for use as the sound absorbing material in an engine exhaust muffler. Preferably, the material is made of glass fibers of E glass compositions. With this invention, the strands are fluffed up, not directly in the muffler, but in a cavity that is made of a perforated shell matching the muffler shape. During this operation, a powder binder also is blown in with the fibers. This blowing operation is completed by forcing hot air through the preform which melts or cures the binder and allows it to bond the fibers together.