SILENT SPORT glass wool size: 400 Gr. size: 400 g. All of our exhaust systems require muffler wool apart from the original items for VESPA (PX/T5/smallframe) over time this can get burned or become clogged with oil, due to over rich carburetion. The exhaust becomes stronger and more and more ineffective, therefore, require replacement. It has proven useful in the past to wrap the wool loosely around the central perforated exhaust outlet pipe when rebuilding the muffler assembly.