Abstract: An exhaust muffler which includes a tubular metallic core having at least one layer of fiberglass around the tubular core. The core has a plurality of circumferential slots formed therethrough with the slots arrayed in spirals around the core. Each slot extends in a transverse or circumferential direction on the core, and has a width to length ratio of about 1:3 to about 1:5. A pair of spaced baffle bars are extended diametrically across the core at spaced locations along its length, and are oriented at right angles to each other in respect to the direction of extension across the longitudinal axis of the core.