Roxul Rigid Mineralwool Panels with 4" thickness and 4# density come in 24" x 48" sheets. Sold per box with each box containing 3 individual sheets. These sheets are generally placed on walls or ceilings and covered with acoustical fabric. 4" Thick panels provide a Noise Reduction Coefficient of 1.10. These 4" thick panels are highly recommended for bass trap applications due to their ability to absorb low frequencies (bass).