Here in America Glass Packs used to refer to mufflers using fiberglass packed around a perforated tube. These mufflers, shaped with rounded bullet shaped ends, had a rather mellow sound when the car was cruising but roared when the engine was revved!
ETA-They were straight through mufflers with very little back pressure, which was very important to us "old time drag racers."
Glass packs on a 4-6 cylinder sound awkwardly reminiscent of a boat motor barely digging into the water.
Now on a V8 glass packs just sound NASTY! I mean that in a somewhat good way...It all depends.
As mentioned, glass packs are notorious for having a nice purr at idle and then unleashing audible mayhem past 2K rpms...but what separates glass packs from flowmasters, borlas, etc...is the sound control. Glass packs tend to have a twitchy, sloppy sound which can really turn a person off but some people( such as a teenage boy) enjoy the obnoxious noise regardless.
Glass packs are illegal in my area...as are most loud exhaust systems. Check with your local law enforcement.
Never checked on the legality, it honestly never occurred to me.
LMAO, its a four cylinder- taurus to be exact and we have decided that unless he wants his curfew to be before his sister's bedtime OR he wants to be the one to watch her when she wakes up that he will forgo the glass packs. Now he wants a racing carborator (spelling but I'm too tired to care) put in it.