Depends on the application. In some cases pink fluffy fiberglass works better. If you only have 6" or less and need lots of absorption though, then in those applications mineral wool batts, compressed mineral wool boards, or OC 703/705 rigid fiberglass are the way to go.Yeah fiberglass is no substitute for Roxul mineral wool insulation. It's a night and day difference. I have that in my ceiling and walls in my drum room and it made a HUGE difference even before I put the 5/8 drywall and ceiling up.