1X11X16" High-Density Fiberglass Muffler Re-Pack, This Tight Weave High Density Muffler Packing Is Preferred By 4-Stroke Riders To Control Sound And Backpressure. When Being Installed Can Be Applied To Muffler Core In Layers That Allow For Fine Tuning Of Backpressure That Effects The Torque Curve To Achieve Desired Feel And Performance. Every Muffler Will Need Repacking After Several Hours Of Riding. Quiet Performance Is The Way To Go For Todays Powersports. For Street Or Off-Road Machines.