The present invention provides composite muffler systems formed of a long fiber thermoplastic. Long fiber thermoplastic technology allows the fibers, to maintain a length sufficient to provide structural strength at lower fiber loading. The long fiber thermoplastic material for forming composite muffler systems also provides increased impact strength and creep resistance as well as chemical and thermal resistance. Mufflers molded with long fiber thermoplastics demonstrate improved dimensional stability as compared to known short fiber based moldings. One suitable muffler structure is a multi-piece muffler assembly including at least one long fiber thermoplastic shell section. In accordance with the present invention, the long fiber thermoplastic material and moldings may also be combined with over-molding of preforms of unidirectional or woven inlays, which provide local structural performance. The use of such preforms is particularly suited to use in the manufacture of high temperature, structural articles such as bumper muffler combinations.