Helix High-Density Fiberglass Muffler Packing The Helix High-Density Fiberglass Muffler Packing provides an effective solution for controlling sound and back pressure in 4-stroke mufflers. This high-quality packing material can be applied to the muffler core in layers, allowing for precise adjustments to back pressure. Essential for maintaining optimal performance, the muffler will require repacking after extended hours of riding to ensure continued efficacy. Features: Excellent for use in 4-stroke mufflers Long lasting high temperature fiberglass Peel apart layer design High density needle mat For street and off-road machines