When talking about soundproofing materials, it is most important to differentiate between soundproofing and sound absorption. These two are often confused for the same thing. Soundproofing means to block sound from entering or leaving a space, like to prevent road noise from entering a living area. Sound absorption is intended to enhance the sound in a given room and is what those creating a home theater or recording studio usually desire. Insulation and special windows can be added during construction, while acoustic foam or vinyl can be used in an existing structure.
In either situation, the best materials won't work as well as intended without a great deal of planning. The greatest benefit from the materials is achieved when they are put into place during construction. It is possible to get some benefit out of soundproofing installed post-construction, but not to the extent of a pre-construction plan. That said, there are many options for attempting to soundproof.
When trying to soundproof, insulation can be helpful when used in the proper areas. Floor insulation is an inexpensive and moderately effective way to block sound between the floors of a home or other building. Apartment owners find this a handy method of stifling sound between apartments on different floors. Insulation like rock wool can be placed between the floor joists to absorb some sound. The best insulation for soundproofing in general is cellulose that is sprayed into place.
Soundproof windows are made with special glass that claims to block outdoor noise. The glass panes are specially created and installed to block annoyances like road noise or noisy buildings nearby. They are best coupled with heavy sealing. They can be enhanced with drapes that will help to deaden some additional sound.
Manufacturers of soundproofing materials offer several options that can be placed during construction or after. Open celled foams work particularly well, and can be purchased under the name acoustic foam and can also be used for sound absorption. Soundproofing vinyl, called mass loaded vinyl (MLV), is lightweight and has a higher mass than expected for such a thin material. It is this mass that gives the vinyl its soundproofing capabilities.
Sound absorption is a different monster than soundproofing. Absorption is the type of sound enhancement that is needed for a recording studio, home theater, or conference room. It deadens other noises within that environment and helps to keep the positive noises in the room.
In extreme situations, some homeowners choose to add an extra layer of wall to rooms, referred to as a room within a room. This involves literally building a new frame of floors and walls over the old with space in between. The space absorbs a significant amount of the sound and enhances the quality of the sound within the room. This method is most applicable to recording studios.
Specially constructed foams and sound boards can assist in the absorption of sounds. Some of these foams resemble egg crates, and some low-tech do-it-yourself homeowners choose to use real egg crates in their walls instead. These foams alone won't provide an extreme level of soundproofing or absorption, but they can help.
Sheetrock is perhaps one of the best soundproofing materials. When used in between walls and in conjunction with rock wool insulation, it can truly kill sounds as they attempt to leave or enter a space. It is not a cheap option, however, and is best planned during construction.
Not all claims made by manufacturers of these materials can be backed up up with evidence. If a material sounds too good to be true, it most likely is. Homeowners should not expect a cheap and easy product to block the construction sounds outdoors, although they can expect to use several methods together to get at least some level of relief.