Repacking your muffler is a yearly necessity. Why you say? Because most modern engines produce exhaust gas temperatures that exceed the temperature limits of traditional packing. Once a fiber's temperature limit has been passed, it becomes brittle and breaks down into particles that get blown out of the muffler. Spec 30 is different because it maintains it's strength in temperatures up to 1400F. With proper repacking, your throttle response remains crisp, your power output and fuel efficiency is maximized, and your noise reduction and exhaust tone are maintained. It also provides vibration absorption and baffle support.