There are many different soundproofing materials. And different materials play different roles. And these soundproofing materials are divided into two categories. One is sound absorbing material and the other is sound isolating material.

Sound absorbing material is usually light and porous for absorbing sound. It can absorb reverberation sound and improve tone quality. But it doesn't perform good in noise reduction. 

Sound isolation is isolating the sound transmission from one room to another room. The sound isolation material are usually dense and heavy. For floor sound proofing, the point is to isolate the noise transmitted from floor to ceiling. 

Usually in sound reduction project, the two materials are used at the same time. Sound isloation materials are used to prevent the noise from outside and noise transmission from indoor to outdoor. Sound absorbing materials will be used to improve tone quality. In this way, the noise can be reduced to a large degree.