I'm thinking about using that same stuff in my theater, which is still in the rough framing stage. I've been reading some materials on soundproofing, so I know a little about it.
It's basically made of sound-absorbing fibers, and a typical way to use it is to sandwich it in between two layers of drywall. It can be applied directly to wall studs, if preferred. It's usually used on walls and basement ceilings, and it's purpose is to weaken the sound transmission through walls and ceilings to other areas of the home.
I've never seen or heard comments on whether or not it improves acoustics inside the theater, but I'd love to know. My guess is it will be more absorbent than drywall.
Anyone care to enlighten us as to its acoustic properties other than soundproofing?