Auralex "Mineral Fiber Insulation -4"
"The best way to tighten up a rooms sound and make it more soundproof in the process is to design it right, build it tight and make the partitions as dense as possible. Thats where our specialized Mineral Fiber sound insulation comes in. Its WAY more dense than the pink stuff and is specifically designed for acoustical usage. It yields much better bass trapping, overall absorption, thermal characteristics, moisturer absorption and sound transmission loss (isolation) than any other product weve found.NRC: 1.00 (2 inch and 4 inch) Qty. Per Box: 4 inch - 3 (24 sq. ft.) Flame Retardancy: Class AAdvantages vs. Std. Fiberglass: better sound isolation, better acoustic absorption, lower moisture absorption, better flame spread smoke density, 1200 degree burn point vs. 650 degree."