A sound muffling material for use in combustion engine exhaust mufflers is provided. The material includes volumized fibers retained in compressed form by a material of lower softening temperature than the fibers. When the material is heated by exhaust gases, the material of lower softening temperature is softened allowing the compressed fibers to expand. The fibers may be formed into a knitted fabric retained by a sacrificial thread. The material may be used to support catalyst bricks.