ok how do these work? i heard there is broken fiberglass in there to resonate and become louder with mileage... is this true?

I don't know exactly how they work.. something along the line that the sound goes thru the air pockets in the fibreglass type material and it dampens the sound.. but with glass pack I hear they also restrict some of the airflow as it creates a lot of turbulance in the chamber.

And yes.. glass pack do blow out the tail end over time so later on it will just be a shell.

ok, glasspacks are basically a perforated tube with a larger one around it with fiberglass between the tubes. the some of the exhaust sounds are absorbed into the fiberglass and are quieted. the reason glasspacks tend to get louder as they get older is because the fiberglass burns out after a while, but if the exhaust shop put 2 glasspacks on your car then the glasspacks should last longer, rather than having just 1. by the way can i see a picture of how the exhaust shop did your glasspacks?