A muffler is a device that is used to reduce the noise emitted by an engine. The material inside a muffler plays an important role in reducing noise. There are two types of materials that are commonly used in mufflers: fibrous and porous.
Fibrous materials, such as fiberglass, are effective at absorbing sound waves. This is because the fibers are able to create many small air pockets that dissipate the energy of the sound waves. Porous materials, such as ceramic, have a similar effect but work by allowing the sound waves to pass through small pores in the material.
While both types of materials are effective at reducing noise, fibrous materials tend to be more durable and have less of a chance of cracking over time. For this reason, most mufflers use a combination of both fibrous and porous materials to achieve optimal results.