what to put in the air gap

Hi everyone, I'm building a big studio in Indiana. Were doing rooms in rooms. My question is, I've got a 6" airgap between all of the walls. Should I fill it with blown in insulation, or should I put absoring blankets in the space? or nothing at all? Each wall is made lead fiber and 2 layers of 5/8 rock Thanks so much for all of your help Jeff Anderson www.lafayettestudio.com

What's the lead fiber? No insulation would be bad. Consider 2.5 pcf to 3.0pcf rigid rockwool, like Roxul's Safe n Sound product. It doesn't have to fill the entire 6". It does have to cover every bit of the wall (no holes where you can see one leaf from the other leaf).

Hi Jeff, I would put insulation into your stud cavities (in 2X4s put 4" thick insulation) and leave the rest of the space between walls empty.. good luck edit: or if you have much insulation left over, maybe just throw it in ?