Insulation is material that restricts the flow of heat, sound, or electric current within a specific area. In homes and other buildings, insulation reduces the flow of heat outward during cold weather and inward during hot weather. In industry, insulation helps maintain certain temperatures necessary for processes used in manufacturing and other operations. The walls of refrigerators and walk-in coolers are also filled with insulation.
This article discusses the use of insulation to control heat flow and to limit the spread of sound. For information about insulation against electric current, see Insulator, Electric .
Insulation to control heat flow
Heat flows from a warmer area to a cooler one by means of (1) conduction, (2) convection, and (3) radiation. Insulation reduces this natural movement (see Heat (How heat travels) ). .
Materials used for insulation include fiberglass, metal foil, rock wool fibers (also called mineral wool), and certain plastics. These materials are poor conductors of heat. When placed against a heated or cooled surface, they provide a barrier to the flow of heat. In addition, most insulation materials are designed to have cell-like spaces that reduce the motion of hot or cold air.
In buildings,
insulation is installed in the areas where the greatest heat loss or heat gain occurs. In most homes, these areas are the ceiling of the top or attic floor, the ceiling of an unheated basement, and the side walls. Insulation for the side walls is installed in the space between the interior and exterior walls. If a basement is heated, its side walls should be insulated.
Almost all insulation needs a vapor barrier to prevent moisture from penetrating the insulation and decreasing its effectiveness. A vapor barrier can be a sheet of foil, plastic, or treated paper. It must be put on the side of the insulation that faces the area with high moisture.
The effectiveness of an insulation material is designated by its R-value, a measurement of the material’s resistance to the flow of heat. Materials with high R-values have the greatest heat flow resistance. Buildings in cold climates require greater resistance to heat flow than do structures in warm areas. Insulation that is properly installed and has an adequate R-value can greatly reduce the amount of energy required to heat or cool a building.
Insulation should be fire-resistant or covered with fire-resistant materials. It should be able to resist any physical or chemical changes that could reduce its effectiveness. It should also be resistant to insects and rodents.
There are five chief kinds of insulation for buildings: (1) batts and blankets, (2) loose-fill insulation, (3) spray foam insulation, (4) rigid insulation boards, and (5) reflective insulation.
Batts and blankets
are soft, flexible units made of fiberglass or rock wool fibers. Batts are cut to certain widths by the manufacturer. Blankets are sold in long rolls that can be cut to any length during installation. Batts and blankets are used between the joists, the beams that support the floor and ceiling, and between wall studs, which are vertical supports in the building frame.
Loose-fill insulation
consists of short fibers of fiberglass, rock wool, or cellulose, or small particles of perlite or vermiculite. It can be blown or poured into attics. It is installed in exterior walls by blowing it through small holes in each stud cavity.
Spray foam insulation
is injected into wall, floor, ceiling, or roof cavities. The foam expands to entirely fill the cavities. It can also be sprayed onto interior surfaces before they are covered with wallboard, flooring, or ceiling panels. Spray foams are expensive, but they leave no gaps around odd shapes. Most spray foams are plastics.
Rigid insulation boards
are made from such materials as fiberglass, gypsum, perlite, and plastic foams. They can be attached to the ceiling, roof, or walls with large-headed nails or adhesives.
Reflective insulation
consists of thin sheets of aluminum foil that reflect heat. The reflective sheets are placed between joists and wall studs. They can also be placed above the ceiling in the attic space.
In industry,
insulation plays an important part in various operations. For example, some industrial furnaces are lined with blankets that resemble those used in home insulation. Industrial insulation blankets are made of ceramic fibers and can withstand temperatures as high as about 2400 °F (1300 °C). These blankets reduce the flow of heat from a furnace so that high temperatures can be maintained during the heating process.
Furnaces used in steelmaking are insulated with ceramic bricks that can endure temperatures up to about 3600 °F (2000 °C). The bricks prevent the hot molten metal inside the furnace from damaging the furnace’s metal parts. Ceramic insulation must also withstand sudden changes in temperature and many types of chemical reactions.
Insulation is also used to maintain certain temperatures in pipelines that transport hot or cold substances. For example, fiberglass insulates the Trans-Alaska Pipeline, which carries hot crude oil a distance of about 800 miles (1,300 kilometers). This insulation helps maintain the high temperatures needed to pump crude oil through the pipeline. It also prevents the heat of the oil from damaging the surrounding frozen land.
Insulation against sound
Insulation against sound is used in buildings to reduce noise. Some types of such insulation block sound and thus prevent it from passing from one room to another. Insulating against heat also typically insulates against sound, because sound travels along the same paths through a building as does heat. Other kinds of insulation against sound absorb sound, thus reducing the noise level within a room. See Acoustics .
Thick, heavy walls without cracks block such sounds as loud music and noisy conversation. But many modern buildings have thin, lightweight walls through which sound can easily pass. In such cases, sound-deadening boards made of wood fibers can be installed in the walls and ceilings. Such insulation must cover the entire surface because even a small gap allows much sound to pass through. Carpeting and other floor coverings help block the passage of sound to rooms below.
Noise in a room may be reduced by carpeting, draperies, and upholstered furniture, all of which absorb sound. For additional sound absorption, acoustical tiles may be installed on the ceilings and walls. These tiles have tiny holes that trap sound and prevent it from bouncing back into the room.
In industry, insulation against sound reduces noise in factories and in machines used at construction sites. Some factories have sound barriers between the workers and the machines. In others, sound-absorption materials are molded to the machines to lower their noise level. Insulation is also used to reduce noise in such construction machines as air compressors and pneumatic drills. Hard rubber pads or heavy mounting springs can be used to insulate—or isolate—the vibrations from motors for fans, which can cause distracting noises.
