There are two broad categories of approaches you use when dealing with sound. One is controlling sound transmission, and the other is shaping/controlling diffusion. In general these types of foams act as diffusers, which influences the sound inside the room, but have very little impact on sound transmission, which is what most people think of when they say 'sound proofing'. Dealing with sound transmission generally requires lots of mass, isolation, and careful attention of air-tightness. Think about how a thermos is constructed and you start to get the idea.
