There are many ways to soundproof a room using noise absorbers that absorb reflected sounds within the room. One material that can be used for this purpose is cork, which is an effective material for removing reflected sound of almost any frequency. Its light weight makes it relatively easy to cut and use in any environment.
NRC stands for Noise Reduction Coefficient and is used to determine how effective a material is at absorbing sound. The closer a materials NRC is to zero, the more effective it is. For instance, a dense material like brick has an NRC between zero and 0.2. Cork floor tiles with a thickness of 3/4-inch have an NRC between 0.10 and 0.15. Cork wall tiles with a 1-inch thickness have an NRC between 0.3 and 0.7, making it very effective at absorbing sound.
Though cork is effective for use in soundproofing, it has a relatively low density and weight when compared to materials with a similar NRC. The reason for this is that cork's cellular structure contains millions of tiny air pockets that decrease the density of the material. A 1-inch piece of cork contains more than 200 million of these air pockets. The result is a material that sound cannot pass through, but is still very lightweight.
Cork is impermeable to both liquids and gases, so it can be used to seal a room both acoustically and in terms of insulation. Cork also resists moisture created by condensation and does not rot; therefore, it does not need to be replaced. This means that cork can be installed under other wall materials and hidden from view without the risk of it quickly degrading over time.
Cork has a low conductivity because of its cellular structure. This has added bonuses such as resistance to fire and heat, but also factors into sound absorptions. Since sound waves are not conducted by the cork material, they deaden very quickly, even if the piece of cork that you are using is not thick. Again, this contributes to the effectiveness of using cork underneath other wall material as a way of making a room soundproof.