What about this stuff? you can get it at home depot.
Ultratouch(#100656748) which look like original carpet insulation found in cars but has a tin foil backing that looks like it would work well to insulate and sound proof...plus it is fire retardant some what....it is $22 for a 4'x8' sheet. or $60 for 24'. It is made by bond logic and is also sold at JC whitney and Summit Racing according to their website.
Here are some of the specs.
UltraTouch™ Radiant Barrier
The UltraTouch Natural Cotton Radiant Barrier Thermal/Acoustic Insulation is an extremely versatile and superior performing product that can be used in automobiles, trucks, buses, RV's, boats, aircraft, residential and commercial building.
The UltraTouch Natural Cotton Radiant Barrier brings fire, fungi, and corrosive resistance to an insulation product that is formaldehyde and resin-free.
In addition, it's natural fibers provide a non-itch padding that is easy to handle and install.
The pure aluminum barrier used for the UltraTouch Natural Cotton Radiant Barrier provides exceptional protection from air currents, vapors, moisture, and radiant heat.
Use this product as a: Radiant Heat Barrier, Acoustic Sound Barrier, Airflow Barrier, Thermal Heat Barrier.