The muffler in your vehicle serves one main purpose; to quiet the natural sound made by internal combustion engines. Mufflers come in all sizes and applications, from the stock quiet one, to the throatier sound of a performance muffler. There are basically two types of mufflers; noise canceling and material packed. In the noise canceling (usually performance) barriers are welded into the muffler to reflect the sound back into itself to cancel it out. In a material style there is a packing, usually around a perforated tube that dampens the sound.