SILENT SPORT glass wool size: 500 Gr. size: 500 Gr. All our exhaust systems require muffler wool apart from the original Vespa items (PX/T5/smallframe) over time this can be burnt out or become clogged with oil, due to excess rich carburetion. The exhaust fumes becomes louder and more and more ineffective, therefore, requiring replacement. It has proven useful in the past to wrap wool loosely around the central perforated exhaust outlet pipe when rebuilding the muffler assembly.