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of AFB here to save money and waste.
Acoustical Fire Batts, or AFB, is a mineral wool manufactured by Roxul with a density of 2.5 pounds per cubic foot. Product dimensions are 24" x 48" x 1" inch. Higher densities absorb sound only slightly better than at 2.5 pcf, but most cost a lot more. Therefore, the 2.5 pcf is the most cost-effective density for absorbing sound.
AFB is flexible, like dense household insulation batts, and it does not hold it’s shape like rigid fiberglass board (such as Owens Corning 703). AFB is suitable for acoustic insulation inside walls, building into panels, or any place where there is a frame or structure to attach it to.
If you need 12 pieces or more, try Roxul AFB Mineral Wool Case of 12.
For more detailed information, see Selecting the Right Acoustic Material for a comparison of these materials.