A muffler assembly including one or more exhaust pipe(s), a polymeric housing carried by at least one of the exhaust pipe(s); a thermal insulating layer lining the housing interior surface and extending between the housing and exhaust pipe at the housing-exhaust pipe interface; wherein the thermal insulating layer includes a nonwoven fabric; wherein when the fabric is exposed to heat, the fabric increases in thickness to seal the muffler assembly at the housing-exhaust pipe interface and provides thermal insulation to the polymeric housing.