In the process of improving the acoustics of the LVL1 Classroom we developed some acoustic panels made largely from reclaimed materials. The frame is made from reclaimed wood from pallets, the cover is a reclaimed coffee bag and they are filled with denim insulation that contains 80% post-consumer recycled content.
Details on the insulation used can be found here
The coffee bags are sprayed with the flame retardant found here
Here are the acoustic properties:
To get an feel for how these panels compare to other insulation options the following link from ATS Acoustics is helpful: Selecting the Right Acoustic material
For even more data on absorption co-efficients check out Bob Golds Apsorption Coefficient Table
As the data indicates, the Ultratouch insulation compares quite favorably to most alternatives even edging out 4" Owens Corning 703 which is a top choice for acoustic panels.
To get an idea for how many panels it would take to achieve the desired reverberation time for a room, try the ATS Acoustics Calculator and select the 2' x 4' option, 4" thick.