The glasspack is an old, simple, and relatively inexpensive muffler design that has less
back pressure than other types of muffler, but is less effective at muffling noise. A longer glasspack will reduce noise to a greater extent than a shorter one, as sound is dissipated into the fiberglass damping material. Other glasspack mufflers have perforated
louvers punched into the center core, which can reduce total flow capacity. The turbulence created by the perforated louvers therefore achieves greater muffling capacity at the expense of total volume of air flow. The more turbulence created, the greater the muffling and less total air flow / power production capacity. Depending on the directionality of the louvers, one can choose between slightly higher flow capacity or slightly greater muffling. This lower flow but slightly quieter design approach is commonly used in glasspack mufflers. Some modern muffler designs are similar in principle to the glasspack, but use more sophisticated sound-absorbing materials such as
stainless steel mesh, and more advanced acoustic engineering, reducing noise while retaining the power-preserving advantages of a straight-through exhaust flow. ==Legality==