According to :
Chris Lewis wrote:

Ask your contractor if he can do rockwool (eg: Roxul).

Generally it's the same price as fiberglass, but is slightly
superior in all respects. Particularly that it's a lot less
picky and less likely to blow around. Can be blown or used as batts.

Can you elaborate on why it's slightly superior? Thanks!

I'm speaking of Roxul here, I'm not familiar with other brands.
The Roxul product is manufactured under license from a European
company IIRC, and is somewhat different than the (much older)
forms of rock wool I've encountered.

Roxul is quite popular in Canada and I believe it's becoming
more popular in the US.

The R value is slightly higher than fiberglass (R21.5 vs R20 I
think for 5.5" batts).

It's heavier, and is a better sound barrier.

The fibers are larger and heavier, doesn't "fly" as much during
installation (no clouds of fine particles), and isn't so "picky".
Eg: you won't be breathing the stuff nor itching for days nor finding
it stuck/embedded in everything. Easier to cut. It's much more
pleasant to work with.

[As long as you're not working overhead, it's reasonable to install
rockwool without gloves/skin/breathing/eye protection.]

Even fiberglass will sog/permanently pack down to a certain extent
with moisture. Rock wool won't pack down, and sheds water quicker.

While fiberglass isn't flammable, the binders are, and the stuff melts
fairly readily. Rockwool has no binders, and the melt point is
considerably higher. Rockwool is thus considerably more fire resistant
than fiberglass.

Here (Roxul is big in Canada), the price per square foot is
usually identical to fiberglass. Most people who try Roxul won't
go back to fiberglass. We had roof insulation upgraded with
blown in (shredded batts) Roxul, and there was virtually _no_
dust anywhere, and I wouldn't think of using anything else. I've
also helped insulate a church extension (about 500 square feet)
with batts, and it was much nicer than previous fiberglass jobs.

About the only drawback to rockwool is that it doesn't compress
as much as fiberglass, so your order will consume more shipping/
storage space.

I have no relationship to the Roxul company, other than as a
satisfied customer ;-)
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
It's not just anyone who gets a Starship Cruiser class named after them.