There are two sides to the acoustical coin if you will. There are products that absorb echo within a room, and there are products that will block or stop/reduce sound transmission. (There are some panels that will do a bit of both. These are generally called composites, but for now, let’s keep it simple.) Echo absorbing materials are used to improve the sound quality inside of the room in which they are installed.  They are usually installed on the walls or ceiling as a finished surface in the room. Products that are used to block sound are used INSIDE of the wall or ceiling - as part of the construction material. They can be dense, heavy materials or materials that will decouple the wall assembly - and due to their density, often reflect the sound back into the room rather than the sound penetrating through to the other side. Absorbing the echo in a room and blocking or reducing sound are done in two very different ways and with different products and approaches.