Some common materials that absorb sound well and that can aid in noise reduction are carpeting, gypsum wall board, mineral fiber ceiling tiles and fiberglass ceiling tiles. Materials that contain a greater degree of mass tend to be the better sound absorbers, but this may not hold true for low-frequency sounds, which are difficult to block and will also curve around barriers. Porous materials, such as cork and foam rubber, are effective in reducing sound transmission because of the decoupling effect produced by their internal air spaces.
Specialized materials can be used for applications that require more than the usual degree of sound reduction, such as acoustical foam rubber baffles attached to the walls and ceiling of an anechoic chamber. Another example of a specialized application is constructing the walls of a gym using concrete blocks with slotted cores to lessen the sound of ball impacts.
An important factor in soundproofing or noise-reduction is choosing a sound-absorbing media that best matches the frequency range of the sound that needs to be attenuated. Lower-frequency sounds can pass through thinner materials easily, while higher frequency sounds are reflected. A combination of carpeting and fiberglass ceiling tiles usually works well for lowering the overall sound levels of people speaking on the phones in an office environment.