In essence, sound proof insulation is the insulation material that is specially designed and used to do the work of a sound or acoustic barrier. A sound barrier is to absorb the unneeded sound from other places. This will also reduce the noise leakage from one room to another.

For some time, mineral wool (rock wool) and the popular fiberglass are the typical materials used for sound proofing. Sometimes, there are also instances that installers use cellulose or cotton. These materials are the same as those used in heat insulation.

At present, there are several ways to soundproof a wall and insulate it. Also, here are now improvements in the soundproofing industry with products that are now more effective sand cost less than the old methods and materials.

Rigid panels 

Several applications are now favored (and recommended highly) by professional sound proof insulation installers. One is the use of rigid panel style mineral wool or rock wool products. These insulation materials are usually sold as rigid panels and softer batts.

The materials used are similarly sized for use in house interio walls, under the floors and used in insulating the ceiling. These sound proofing panels are available for wood or steel walls and ceilings.

Mineral wool

Among the many materials, mineral wool is known to resist fire, water and moisture because it is made from natural stone fibers. The mineral wool products (Rock board 60 and 80) are also becoming to be multi-purpose insulation products. Their thermal insulating capabilities are found to be very good.

Unfortunately, their sound absorbing performance is a bit lower than expected. However, these products are capable of being used in the inside to sound proof the exterior walls while capable of being a standard thermal insulation by itself.

They have many qualities for both high and low frequency sounds, and are fit for framed or covered panels.

Fiberglass

Mineral wool and fiberglass soundproofing insulation is available around and can be bought in packages of multiple panels. Both are made with good tolerances and can fit snugly in between wall studs and ceiling joints.

Both fit into cavities with a friction press fit, all of which ensures that there will be no air gaps for sound to leak into the adjoining rooms. These insulation panels and are rigid enough to be cut into shape around electrical outlets and studs. 

Drywell saws are used to cut out the precise notches in making each panel fit into place. The walls and the ceilings are finished off with a standard or soundproof grade drywall.

Qualities

The sound-absorbing capabilities (and performance) of both fiberglass and mineral wool are similar. The prices are not similar, though, even if they are of the same thickness.

As a good alternative to mineral wool, fiberglass is very good. It can do both types of insulation: it is a good thermal insulation material as well as a good material for soundproofing.  

Cotton insulation used for soundproofing also provides a very good performance in sound absorption. Cotton, like the other batt materials is soft, which would need the support of a frame or covering. There are alternatives now for use in sound proof insulation.