The usual stuff is wall insulation with R value I do not know.

I need to repack mine anybody have any idea with R-value to use with a Hall-n-a$$ pipe?

I think they use the insulation to protect the pipe in shipping not to pack the silencer 

I always use  the stuff made by fmf and it is way more dense than the insulation for walls

Density isn't always a good thing though.
If the packing material cannot compress, then it also cannot deaden the sound.
A very loosely packed silencer will reduce db levels considerably, but it won't last very long.

The trick is not to increase density, but to increase the springiness of the packing material.
If the material will compress to a high degree, it will absorb more sound, and if it springs back to fill the silencer then it will continue to work well.
The problem is, most packing materials don't spring back out as well as needed...so you have to pack more stuff in there.
Higher density stuff has less compressibility, so you have to stuff more in and reduces the effectiveness of the silencer.

Supposedly, the stuff from 500Fanatic was far superior to the standard packing available now.

The last stuff I used I got from Aaen performance.Not sure who supplies them.