Fiberglass muffler packing can improve performance in several ways:

1. Improved Exhaust Flow: Fiberglass packing materials are designed to withstand high temperatures and effectively dampen sound without restricting exhaust flow. This helps in maintaining optimal engine performance by reducing back pressure.

2. Sound Control: By absorbing and muffling sound waves, fiberglass packing reduces the noise produced by the exhaust system. This is particularly beneficial for vehicles where noise reduction is desired without sacrificing performance.

3. Durability: Fiberglass is known for its durability and heat resistance. It can withstand the high temperatures generated by exhaust systems without degrading quickly, ensuring longevity and consistent performance.

4. Weight Reduction: Compared to some alternative materials, fiberglass can be lightweight. This reduction in weight can contribute to overall vehicle performance, especially in terms of handling and acceleration.

5. Maintenance: Properly packed mufflers can improve the lifespan of the exhaust system components by reducing the likelihood of corrosion and damage caused by excessive heat and vibration.

Overall, fiberglass muffler packing helps in balancing performance with sound control and durability, making it a popular choice in aftermarket exhaust systems.