they are the type that has fiberglass in them
Really though i doubt anyone is gonna be able to tell what brand they are anymore seeing as how most glasspacks look the same other than maybe the color that they are painted or not painted. I had glasspacks with 2 inch pipe on my 77 for a while because it was cheap but they eventually started to cackle so i went to my local muffler shop and had 2 1/2 inch duals with Force street strip chambered mufflers put on it dumping in front of the axle and it sounds very good. Its not real loud at an idle but when you open it up its much louder than what the junk glass packs were. No offense to anyone that has them but i think glasspacks are starting to be the muffler of yesterday. Or at least where i'm from. Everyone is going with chambered mufflers because you get that deep throaty roar instead of a loud cackle. Just my $.02
-JEREMY-