What’s the difference between sound absorption material and sound insulation material?

When the reflection of sound absorption on incident sound energy is small, it means that the sound energy can easily access to and penetrate this material: It is can be imaged that this material should be porous, loose and breathable, and it is a typical porous or multi-slot sound absorption material. Its structure is: the material has a large number of millipores with each other connected from surface to interior side, that is to say, it has certain permeability. For sound insulation material, it should reduce sound energy of projection and stop sound spread, so it can not be as porous, loose and breathable as sound absorption material. By contrast, its material should be heavy and compact, e.g. steel plate, lead plate, brick wall, glass, etc. The specific requirements of sound insulation material are: firstly, dense and non-porous; secondly, greater weight.