The choice and degree of insulation is based on a number of factors:
Ease of installation e.g. some materials cannot be retrofitted due to issues of accessibility or toxicity
Durability - resistance to compression, moisture, degradation
Cost - which is generally related to durability and effectiveness
The mode of heat transfer - bulk insulators are most useful in cold conditions where significant convective / conductive losses occur, they are less useful in hot conditions where solar radiation is the source of heat gain. (see Building insulation)[dubious – discuss] Conversely, radiant barriers have a greater role in warm climates.
The orientation of the surface and direction of heat flow determine how effective a radiant barrier will be--radiant barrier work best at stopping downward heat transfer from or to horizontal surfaces.
Toxic effects / Off gassing
Usually a combination of materials are required to achieve an optimum solution for a building over a range of climactic conditions. There are also some products which combine different types of insulation in the one product.
Materials used for insulation
A range of material can be employed in the manufacture and construction of insulation products:
For large-scale applications, a contractor mixes chemicals on site, and sprays or injects expanding foam onto concrete slabs, into wall cavities of an unfinished wall, against the interior side of sheathing, or through holes drilled in sheathing or drywall into the wall cavity of a finished wall.
Can be used in places where loose-fill cannot, such as between joists and rafters. When used between rafters, the spray foam can cover up the nails protruding from the underside of the sheathing, protecting your head.
Can be applied in small quantities.
Cementitious foam is fireproof.
The cost can be high compared to traditional insulation.
Most or all, with the exception of cementitious foams, release toxic fumes when they burn.
Depepnding on usage and building codes, most foams require protection with a thermal barrier such as drywall on the interior of a house. For example a 15-minute fire rating may be required.
Some shrink slightly while curing.
Although CFCs are no longer used, many use HCFCs or HFCs as blowing agents. Both are potent greenhouse gases, and HCFCs have some ozone depletion potential.
Most, such as Polyurethane and Isocyanate insulation, contain hazardous chemicals such as benzene and toluene. These are a potential hazard and environmental concern during raw material production, transport, manufacture, and installation. 
Foam insulations are made from petrochemicals and may be a concern for those seeking to reduce the use of fossil fuels and oil.
R-value will diminish slightly with age, though the degradation of R-value stops once an equilibrium with the environment is reached. Even after this process, the stabilized R-value is very high.
Most foams require protection from sunlight and solvents.
It is difficult to retrofit some foams to an existing building structure because of the chemicals and processes involved.
Advantages of closed-cell over open-cell foams
While both closed-cell and open-cell foams (such as polyurethane, polystyrene, polyisocyanurate, and "Great Stuff") provide an effective air barrier, only closed-cell foams are effective vapor barriers. A continuous air barrier ensures an air-sealed building envelope and thus prevents virtually all air-borne moisture migration through the skin of a building. Basically, a vapor barrier is no longer required.
Closed-cell foams are superior insulators (R-5 to 6 usually, and up to R-8, as opposed to R-3 to 4 for open cell). This is only of relevance if the depth of the cavity is insufficient to accommodate thicker applications of the insulation material. In typical applications, a required R-value is specified. The insulation material is then applied accordingly. Example: most often the requirement for wall insulation is R-13. In this case, one might apply 2 inches of higher density foam with an R-value of 6.5 per inch or 3.5 inches of open-cell foam with an R-value of 3.7.
Higher structural stability
Icynene spray formula.  R-3.6 per inch. Icynene (polyicynene) "does not shrink, sag or settle." Icynene uses water for its spray application instead of any ozone depleting chemicals. Flammability is relatively low. Disadvantages: Expensive. Does not achieve code in all jurisdictions. Smoke is toxic. Polyicynene is a plastic (open cell polyurethane foam) and therefore made from petrochemicals. Contact with skin, eyes, or respiratory system is hazardous during application.  Similar hazards occur during manufacture. Isocyanates are the leading cause of workplace-related asthma and pulmonary disorders in the United States (according to NIOSH & OSHA).
Sealection 500 spray foam.  R-3.8 per inch. So called "water-blown" as it uses water in a chemical reaction to create carbon dioxide and steam which expands the foam. Flame spread is 21 and smoke developed is 217 which makes it a Class I material (best fire rating). Disadvantages: Is an Isocyanate.
Cementitious foam, such as Air-Krete.  R-3.9 per inch. Non-hazardous. Is the only foam not restricted to a depth of application. Fireproof - will not smoke at all upon direct contact with flame; is a four-hour firewall in the State of Connecticut. Great for sound deadening; does not echo like other foams. Environmentally friendly. Non-expansive (good for existing homes where interior sheathing is in place). Fully sustainable: Consists of magnesium oxide and air, made from magnesium oxide extracted from seawater. Blown with air (no CFCs, HCFCs or other harmful blowing agents). Nontoxic, even during application. Does not shrink or settle. Zero VOC emission. Chemically inert (no known symptoms of exposure per MSDS). Insect resistant. Mold Proof. Insoluble in water. Disadvantages: Expensive. Fragile at low densities as are needed to achieve the quoted R value.
Polyisocyanurate, typically R-5.6 or slightly better after stabilization - higher values (R-7 or better) in stabilized boards. Less flammable than polyurethane.
Phenolic. Uses air as blowing agent. Shrinks while curing.
Closed-cell polyurethane. White or yellow. May use a variety of blowing agents. Resistant to water wicking and water vapor.
Open-cell (low density) polyurethane. White or yellow. Expands to fill and seal cavity, but expands slowly, preventing damage to the wall. Resistant to water wicking, but permeable to water vapor. Fire resistant.
Great Stuff is a Dow Chemical product that comes in cans and consists of several complex chemicals mixed together (isocyanates, ether, polyol). Dow manufactures this for small applications, but there is nothing stopping you from buying dozens of cans for a large retrofit task, such as sealing the sill plate. Since the blowing agent is a flammable gas, using large quantities in a short time requires strict attention to ventilation. Toxic vapors are minimal due to low vapor pressure and what little there is should be removed quickly if adequate ventilation is used. However, a respirator with an organic vapor sorbent may be advisable in some cases, for example if the foam is heated  Very thick applications should be done layer-by-layer to ensure proper curing in a reasonable time frame.
Honeywell's Enovate Foam Blowing Agent is an HFC used in some closed-cell spray foam insulations. Although it has zero ozone depletion potential, it has very high global warming potential.
Rigid panel insulation is made from fibrous materials (fiberglass, rock and slag wool) or from plastic foam. They are sometimes sold in sections designed to fit tightly in standard wall cavities. When sold this way, they are called "batts", and they come in different thicknesses to match the depth of wall cavities, for example, approx. 5½ inches to match a 2 x 6 wall cavity.
Where rigid panels are most often used:
Some, such as EPS "beadboard", are suitable for ground contact and are used against footings and exterior backfilled foundation walls.
Against exterior exposed foundation walls (should be coated to protect from sunlight).
Against exterior walls between foundation and roof, installed between sheathing and siding.
Either under or on top of the roof sheathing.
Inside unfinished interior walls, either as pre-cut batts, or as panels cut to fit inside walls and secured in place.
Where space is limited and you need to pack great insulating capacity into a small space.
Important note #1: If you insulate the foundation with rigid panels, but you stop using rigid panels where the siding begins, then you should install flashing in between the bottom course of siding and the top edge of the rigid panels, to prevent water from seeping behind the panels.
Important note #2: When insulating the exterior foundation, you should install the rigid panels in two staggered layers, and fill the gaps at the seams with spray foam, to keep moisture from penetrating from the outside. However, when insulating between the sheathing and siding, you should leave slight gaps between the rigid panels to allow moisture to escape from the exterior side of the sheathing.
High R-value per inch - useful where space is tight or cramped, such as cathedral ceiling.
Protect foundation and damp-proofing during backfilling (and, of course, insulate foundation).
All are lightweight and strong - although EPS can be crumbly.
Add to structural strength of walls.
Provide acoustical insulation as well as thermal.
Most are easily cut with utility knives.
All are water resistant, some more so than others (but none should face prolonged exposure to water).
Will not rot.
XPS type is highly resistant to air infiltration. Can be virtually airtight if installed without gaps between adjacent panels, with seams taped.
Reduce heat conduction through the wall frame when used as sheathing.
Rigid panels with a radiant heat barrier facing foil will significantly improve the insulating properties by reflecting infrared solar energy before penetrating the wall or ceiling.
Some types use some recycled content.
All are susceptible to UV damage and solvents. Building codes require exterior cladding (e.g. stucco) where they are above ground and exposed.
All are flammable and produce toxic fumes when they burn. All of them should be covered with fire-rated drywall (gypsum board) when installed in the interior of a house, unless they have a low flame-spread rating (below 25).
More expensive than most other types of insulation.
Some types may be susceptible to termites using them for nesting purposes.
May have R-values higher than that of still air, if some type of insulating gas was blown into them during manufacturing. For many years, manufacturers used CFCs or urea formaldehyde as blowing agents. These blowing agents eventually leak out of the panels. CFCs deplete the ozone layer, and formaldehyde is toxic. Some manufacturers still use HCFCs, which are still harmful to the ozone layer, but not to the same extent as CFCs. Eventually, as the blowing agent leaks, air replaces the insulating gas, and the R-value of the panel drops.
Most rigid panels are made from crude oil byproducts, and some toxic pollution results during their manufacturing.
Fibreglass and rock wool. These are mainly used for acoustic applications. A company called Roxul in Ontario, Canada uses rock wool as the basis for all of their products, including panels for insulating the exterior foundation. All of their products are naturally fire-resistant. 
Phenolic, also known as phenol-formaldehyde. Advantages: High strength. Less flammable than most other foams. Disadvantages: Material is mostly open-celled. This results in insulating capacity not as good as other foams, high water absorption, and high water vapor permeability. Degrades and releases some formaldehyde over time, but not nearly as much as urea formaldehyde.
Polyurethane. White or yellow. Produced through mixing of isocyanate and polyether in presence of catalyst and blowing agent. Contains many tiny, closed cells. Relatively waterproof, and low water absorption, but must protect from prolonged exposure to water. Can use underground if conditions are relatively dry.
Polyisocyanurate(also known as polyiso). More stable at high temperatures and less flammable than polyurethane. Higher R-value vs. polystyrene and polyurethane due to its gas-filled closed-cell foam structure. Denser and more rigid than polystyrene panels, but more expensive. Must protect from prolonged exposure to water. Usually contains some recycled plastic, such as from PET beverage containers.
Vacuum insulation consisting of thin panels with extreme insulation capacities, as high as R-50 per inch. However, like double-glazed windows, these eventually lose their air-tight seal.
Natural fibre insulations (around 0.04 W/mK) all can be treated with low toxicity fire and insect retardents, often used in Europe
Lightweight Wood Fibre board.
More on rigid cellular polystyrene panels
There are many types of rigid cellular polystyrene (RCPS). Styrofoam is simply Dow Chemical's brand name, and does not refer to any particular type of RCPS. Some polystyrene uses up to 50% recycled resin, including post-consumer plastic. Several states have banned polystyrene that uses CFCs as blowing agents.
Molded expanded polystyrene, also known as MEPS, EPS, or beadboard, consists of many tiny foam beads molded and pressed together. EPS is manufactured in low-density and high-density versions. Low-density EPS is relatively inexpensive, resistant to the effects of moisture, and can be used underground. High-density EPS is even more moisture-resistant, and is manufactured for use on exterior foundation walls and burial against footings, if the soil is relatively dry. EPS typically uses pentane as a blowing agent, avoiding the high global warming potential of CFCs, HCFCs and HFCs, as well as the ozone depletion potential of CFC and HCFCs.
Extruded polystyrene, also known as XPS, or blueboard, has a smooth, cut-cell surface, is stronger than EPS, and is ideal for blocking air-infiltration. Dow Chemical colors their XPS blue and markets it under their global recognized brand "Styrofoam". Like EPS, XPS is also manufactured in low-density and high-density versions. High-density XPS is used for foundation slabs, concrete floors, roofs, and other applications that require higher bearing strength than EPS and low-density XPS. XPS typically uses HCFCs as blowing agents, which have high global warming potential and moderate ozone depletion potential, or HFCs which have high global warming potential even though they have zero ozone depletion potential.
Structural insulated panels
Structural insulated panels (SIPs), also called stressed-skin walls, use the same concept as in foam-core external doors, but extend the concept to the entire house. They can be used for ceilings, floors, walls, and roofs. The panels usually consist of plywood, oriented strandboard, or drywall glued and sandwiched around a core consisting of expanded polystyrene, polyurethane, polyisocyanurate, compressed wheat straw, or epoxy. Epoxy is too expensive to use as an insulator on its own, but it has a high R-value (7 to 9), high strength, and good chemical and moisture resistance.
SIPs come in various thicknesses. When building a house, they are glued together and secured with lumber. They provide the structural support, rather than the studs used in traditional framing.
Strong. Able to bear loads, including external loads from precipitation and wind.
Faster construction than stick-built house. Less lumber required.
Impermeable to moisture.
Can truck prefabricated panels to construction site and assemble on site.
Create shell of solid insulation around house, while reducing bypasses common with stick-frame construction. The result is an inherently energy-efficient house.
Do not require much energy to manufacture.
Do not use formaldehyde, CFCs, or HCFCs in manufacturing.
True R-values and lower energy costs.
More expensive than other types of insulation.
Fiberglass batts and blankets
Batts are precut, whereas blankets are available in continuous rolls. Compressing the material reduces its effectiveness. Cutting it to accommodate electrical boxes and other obstructions allows air a free path to cross through the wall cavity. One can install batts in two layers across an unfinished attic floor, perpendicular to each other, for increased effectiveness at preventing heat bridging. Blankets can cover joists and studs as well as the space between them. Batts can be challenging and unpleasant to hang under floors between joists; straps, or staple cloth or wire mesh across joists, can hold it up.
Gaps between batts (bypasses) can become sites of air infiltration or condensation (both of which reduce the effectiveness of the insulation) and requires strict attention during the installation. By the same token careful weatherization and installation of vapour barriers is required to ensure that the batts peform optimally. Air infiltration can be also reduced by adding a layer of cellulose loose-fill on top of the material.
Rock and slag wool. Usually made from rock (basalt, diabase) or iron ore blast furnace slag. Some rock wool contains recycled glass. Nonflammable. 
Fiberglass. Made from molten glass, usually with 20% to 30% recycled industrial waste and post-consumer content. Nonflammable, except for the facing (if present). Sometimes, the manufacturer modifies the facing so that it is fire-resistant. Some fiberglass is unfaced, some is paper-faced with a thin layer of asphalt, and some is foil-faced. Paper-faced batts are vapor retarders, not vapor barriers. Foil-faced batts are vapor barriers. The vapor barrier must face the proper direction.
Plastic fiber, usually made from recycled plastic. Does not cause irritation like fiberglass, but more difficult to cut than fiberglass. Not used in USA. Flammable, but treated with fire-retardant.
Natural fibre insulations (around 0.04 W/mK), treated with low toxicity fire and insect retardents, are available in Europe: cotton, hemp, flax, coco, and wool, these often mixed with polyester fibers, and lightweight wood fibre, and cellulose (often with polyolefin).
Batts as the common choice of residential insulator
The examples and perspective in this article or section may not represent a worldwide view of the subject. Please improve this article or discuss the issue on the talk page.
Historically, fiberglass batts became the preferred choice for residential construction in the late 20th century; it is useful to understand how this evolved, as there is no inherent advantage to batts. [Commercial and industrial construction do not use batts.] In the 1970s in response to oil price shocks, many US state governments sought to cut home heating oil usage by increasing building code insulation requirements for all new housing. At the same time, Owens Corning fiberglass lobbied intensively to convince the building officials who wrote and administered the four separate building codes then used in the USA. They also aimed to eliminate other kinds of housing insulation material (such as polyurethane) on safety or hazard grounds. The result was that Owens Corning successfully lobbied for mandatory 2" x 6" (50 x 150 mm) wall framing with fibreglass insulation. This suited timber merchants just as well as it suited Owens Corning. Then, given the predominance of non-wind-proof cladding materials, and the prevalence of sleet (wind-blown ice) during the winters of the northern states, a need was created to ensure the whole 150 mm of fibreglass stayed ice-free and dry at all times. Building code officials also made it mandatory to fix and seal wind-and-sleet-proof plywood sheathing under all claddings. This suited the plywood industry very well - which in turn led to the North American development of its now-massive oriented strand board (OSB) industry.
Other insulation materials present advantages in terms of stopping air, moisture migration, and recycling for sustainability not found in fiberglass batts.
Cotton Batts ( Blue Jean insulation)
Cotton insulation is increasing in popularity as a environmentally preferable option for insulation. It has an R-value of around 3.7, a higher value than most fiberglass batts. The cotton is primarily recycled industrial scrap, providing a sustainability benefit. The batts do not use the toxic formaldehyde backing found in fiberglass, and the manufacture is nowhere near as energy intensive as the mining and production process required for fiberglass. Boric acid is used as a flame retardant, and is compared to table salt in terms of human toxicity. A small quantity of polyolefin is melted as an adhesive to bind the product together (and is preferable to formaldehyde adhesives). Installation is similar to fiberglass, without the need for a respirator but requiring some additional time to cut the material. As with any batt insulation, proper installation is important to ensure high energy efficiency.
Loose-fill (including Cellulose)
Loose-fill materials can be blown into attics, finished wall cavities, and hard-to-reach areas. They are ideal for these tasks because they conform to spaces and fill in the nooks and crannies. They can also be sprayed in place, usually with water-based adhesives. Many types are made of recycled materials and are relatively inexpensive.
General procedure for retrofits in walls:
Drill holes in wall with hole saw, taking firestops, plumbing pipes, and other obstructions into account. It may be desirable to drill two holes in each wall cavity/joist section, one at the bottom and a second at the top for both verification and top-off.
Pump loose fill into wall cavity, gradually pulling the hose up as the cavity fills.
Cap the holes in the wall.
Cellulose insulation is environmentally preferable (80% recycled newspaper) and safe. It has a high recycled content and less risk to the installer than fiberglass (loose fill or batts).
R-Value 3.4 - 3.6 per inch (imperial units)
Loose fill insulation fills the wall cavity better than batts. Wet-spray applications typically seal even better than dry-spray.
Class I fire safety rating
No formaldehyde-based binders
Not made from petrochemicals nor chemicals with a high toxicity
Doesn't seal bypasses as well as closed-cell foams do, though wet-spray applications come close.
Weight may cause ceilings to sag if the material is very heavy.
Will settle over time, losing some of its effectiveness. Unscrupulous contractors may "fluff" insulation using fewer bags than optimal for a desired R-value. Dry-spray (but not wet-spray) cellulose can settle 20% of its original volume. However, the expected settling is included in the stated R-Value.
R-values stated on packaging are based on laboratory conditions; air infiltration can significantly reduce effectiveness, particularly for fiberglass loose fill. Cellulose inhibits convection more effectively. In general, loose fill is seen as being better at reducing the presence of gaps in insulation than batts, as the cavity is sealed more carefully. Air infiltration through the insulating material itself is not studied well, but would be lower for wet-spray insulations such as wet-spray cellulose.
Rock and slag wool, also known as mineral wool or mineral fiber. Made from rock (basalt, diabase), iron ore blast furnace slag, or recycled glass. Nonflammable. More resistant to airflow than fiberglass. Clumps and loses effectiveness when moist or wet, but does not absorb much moisture, and regains effectiveness once dried. Older mineral wool can contain asbestos, but normally this is in trace amounts.
Cellulose insulation. Cellulose, like rock wool, is denser and more resistant to air flow than fiberglass. Persistent moisture will weaken aluminium sulphate flame-retardants in cellulose which are widely used in the USA. However, in Australia borax fire retardant, comprised of boric acid & borax decahydrate, has been in use for more than 30 years and is not affected by moisture in any way. Dense-pack cellulose is highly resistant to air infiltration and is either installed into an open wall cavity using nets or temporary frames, or is retrofitted into finished walls. However, dense-pack cellulose blocks, but does not permanently seal, bypasses, as a [[Thermal insulation spray foams (foam-in-place) closed-cell foam would. Furthermore, as with batts and blankets, warm, moist air will still pass through, unless there is a continuous near-perfect vapor barrier. Wet-spray cellulose is cellulose mixed with water and adhesive to help the cellulose bind to the inside of open wall cavities, and to make the cellulose more resistant to settling. Wet-spray cellulose must be allowed to dry completely before sealing up the wall with a vapor barrier and drywall. Moist-spray cellulose uses less water to speed up drying time. Cellulose insulation is regulated as a recognized fire hazard by the Consumer Product Safety Commission (CPSC), which requires labeling of cellulose insulation to inform installers and consumers about the threat of fire. (See 16 C.F.R. 1209, 1404)
Fiberglass. Usually pink, yellow, or white. Loses effectiveness when moist or wet, but does not absorb much water. Nonflammable. See Health effects of fiberglass.
Natural insulations such as granulated cork, hemp fibres, grains, all which can be treated with a low toxicity fire and insect retardants
Cotton, wool, hemp, corn cobs, strawdust and other harvested natural materials. Not common.
Granulated cork. Cork is as good an insulator as foam. It does not absorb water as it consists of closed cells. Resists fire. Used in Europe.
Wood chips, sawdust, redwood bark, hemlock fiber, or balsa wood. No longer used. Wood absorbs water, which reduces its effectiveness as a thermal insulator. In the presence of moisture, wood is susceptible to mold, mildew, and rot.
U.S. regulatory standards for cellulose insulation
16 CFR Part 1209 (Consumer Products Safety Commission, or CPSC) - covers settled density, corrosiveness, critical radiant flux, and smoldering combustion.
ASTM Standard C-739 - loose-fill cellulose insulation - covers all factors of the CPSC regulation and five additional characteristics, R-value, starch content, moisture absorption, odor, and resistance to fungus growth.
ASTM Standard C-1149 - Industry standard for self-supported spray-applied cellulose insulation for exposed or wall cavity application - covers density, R-value, surface burning, adhesive strength, smoldering combustion, fungi resistance, corrosion, moisture vapor absorption, odor, flame resistance permanency (no test exists for this characteristic), substrate deflection (for exposed application products), and air erosion (for exposed application products).
16 CFR Part 460 - (Federal Trade Commission regulation) commonly known as the "R-Value Rule," intended to eliminate misleading insulation marketing claims and ensure publication of accurate R-Value and coverage data.
Skylights, solariums and other special applications may use aerogels, a high-performance, low-density material. Silica aerogel has the lowest thermal conductivity of any known substance, and carbon aerogel absorbs infrared radiation (i.e. heat from sun rays) while still allowing daylight to enter. The combination of silica and carbon aerogel gives the best insulating properties of any known material, approximately twice the insulative protection of the next best insulative material, closed-cell foam.
Main article: Straw-bale construction
The use of highly-compressed straw bales as insulation, though uncommon, is gaining popularity in experimental building projects for the high R-value and low cost of a thick wall made of straw. "Research by Joe McCabe at the Univ. of Arizona found R-value for both wheat and rice bales was about R-2.4 per inch with the grain, and R-3 per inch across the grain. A 23" wide 3 string bale laid flat = R-54.7, laid on edge (16" wide) = R-42.8. For 2 string bales laid flat (18" wide) = R-42.8, and on edge (14" wide) = R-32.1" (Steen et al.: The Straw Bale House, 1994). Using a straw bale in-fill sandwich roof greatly increases the R value. This compares very favorably with the R-19 of a conventional 2 x 6 insulated wall. When using straw bales for construction, the bales must be tightly-packed and allowed to dry out sufficiently. Any air gaps or moisture can drastically reduce the insulating effectiveness.
These materials reduce radiation of heat to or from the surface of the material, rather than heat conducted through the material. For this reason, trying to associate R-values with radiant barriers is difficult and inappropriate. The R-value test measures heat transfer through the material, not to or from its surface. There is no standard test designed to measure the reflection of radiated heat energy alone. Radiated heat is a significant means of heat transfer; the sun's heat arrives by radiating through space and not by conduction or convection. At night the absence of heat (i.e. cold) is the exact same phenomenon, with the heat radiating described mathematically as the linear opposite. Radiant barriers prevent radiant heat transfer equally in both directions. However, heat flow to and from surfaces also occurs via convection, which in some geometries is different in different directions.
Foil or foil laminates.
Foil-faced polyurethane or foil-faced polyisocyanurate panels.
Foil-faced polystyrene. This laminated, high density EPS is more flexible than rigid panels, works as a vapor barrier, and works as a thermal break. Uses include the underside of roof sheathing, ceilings, and on walls. For best results, this should not be used as a cavity fill type insulation.
Foil-backed bubble pack. This is thin, more flexible than rigid panels, works as a vapor barrier, and resembles plastic bubble wrap with aluminum foil on both sides. Often used on cold pipes, cold ducts, and the underside of roof sheathing.
Light-colored roof shingles and reflective paint. Often called [[cool roofs], these help to keep attics cooler in the summer and in hot climates. To maximize radiative cooling at night, they are often chosen to have high thermal emissivity, whereas their low emissivity for the solar spectrum reflects heat during the day.
Metal roofs, e.g. aluminum or copper.
Radiant barriers can be combined with vapor barriers.
Materials with one shiny side must be positioned with the shiny side facing an air space to be effective.
Insulation no longer used
Urea-formaldehyde foam (UFFI) and panels
Most states have outlawed urea-formaldehyde insulation since the early 1980s because it releases formaldehyde gas, causing indoor air quality problems. The chemical bond between the urea and formaldehyde is weak, resulting in degradation of the foam cells and emission of toxic formaldehyde gas into the home over time. Furthermore, some manufacturers used excess formaldehyde to ensure chemical bonding of all of the urea. Any leftover formaldehyde would escape after the mixing. Since emissions are highest when the urea-formaldehyde is new and decrease over time, houses that have had urea-formaldehyde within their walls for years or decades do not require remediation.
UFFI is an inexpensive and high R-value insulator that regains effectiveness when dried after having absorbed moisture. Its open-cell structure is a good acoustic insulator. It provides little mechanical strength, as the material is weak and brittle. Water and vapor permeates it easily. See  and 
Asbestos once found common use as an insulation material in homes and buildings because it is fireproof, a good thermal and electrical insulator, and resistant to chemical attack and wear. We now know that asbestos can cause cancer when in friable form (that is, when likely to release fibers into the air - when broken, jagged, shredded, or scuffed). Only some people exposed to asbestos develop cancer. The recommended course of action if you find asbestos in your house is to enclose (shield) and encapsulate (seal). Asbestos-cement shingles are harmless unless they are flaking, or you saw or break them.
When found in the home, asbestos often resembles grayish-white corrugated cardboard coated with cloth or canvas, usually held in place around pipes and ducts with metal straps. Things that typically might contain asbestos:
Boiler and furnace insulation.
Heating duct wrapping.
Pipe insulation ("lagging").
Ducting and transite pipes within slabs.
Roofing materials and felts.
Health & safety issues
Fiberglass is the most common residential insulating material, and is usually applied as batts of insulation, pressed between studs. Health and safety issues include potential cancer risk from exposure to glass fibers, formaldehyde off-gassing from the backing/resin, use of petrochemicals in the resin, and the environmental health aspects of the production process. Green building practices shun Fiberglass insulation.
The World Health Organization has declared fiber glass insulation as potentially carcinogenic.
The product is still required to carry a cancer warning label in the USA.
Fiber glass is now the most thoroughly evaluated insulation material in the market. The fiber glass insulation industry is committed to ensuring that fiber glass products can be safely manufactured, installed and used. This industry has funded tens of millions of dollars of research at leading independent laboratories and universities in the United States and abroad. The weight of the scientific research shows no association between exposure to glass fibers and respiratory disease or cancer in humans.
In October 2001, an international expert review by the
International Agency for Research on Cancer (IARC) re-evaluated the 1988 IARC assessment of glass fibers and removed glass wools from its list of possible carcinogens by downgrading the classification of these fibers from Group 2B (possible carcinogen) to Group 3 (not classifiable as to carcinogenicity in humans). All fiber glass wools that are commonly used for thermal and acoustical insulation are included in this classification. IARC noted specifically: "Epidemiologic studies published during the 15 years since the previous IARC Monographs review of these fibers in 1988 provide no evidence of increased risks of lung cancer or mesothelioma (cancer of the lining of the body cavities) from occupational exposures during manufacture of these materials, and inadequate evidence overall of any cancer risk."
The IARC downgrade is consistent with the conclusion reached by the U.S. National Academy of Sciences, which in 2000 found "no significant association between fiber exposure and lung cancer or nonmalignant respiratory disease in the MVF [man-made vitreous fiber] manufacturing environment."
However, the literature should be considered carefully before determining that the risks should be disregarded. The OSHA chemical sampling page provides a summary of the risks, as does the NIOSH Pocket Guide.
Miraflex is a new type of fiberglass batt that has curly fibers that are less itchy and create less dust. You can also look for fiberglass products factory-wrapped in plastic or fabric.
Fiberglass is energy intensive in manufacture and fibers are wrapped in oil-based resins. Fiberglass batts are typically backed with formaldehyde, a hazardous chemical known to slowly off-gas from the insulation over many years.  The industry has tried to mitigate these issues. Formaldehyde-free batts (which actually contain a very low amount of formaldehyde) and batts made of some recycled fiberglass (up to 30% recycled content) are available.
Cellulose is 100% natural and made from recycled newsprint. Health issues appear to be minor, and most concerns over the flame retardants and mold potential seem unfounded.
Cellulose is treated with a flame retardant and insect repellent, usually boric acid and sometimes borax to resist insects and rodents. Some people think that the chemicals, dust, and newspaper ink in cellulose may be harmful to breathe and touch, though studies do not show this.
Mold has been seen as a potential concern. One thing that has not contributed to mold problems is the growing popularity of cellulose insulation among knowledgeable home owners who are interested in sustainable building practices and energy conservation. Mycology experts (mycology is the study of mold) are often quoted as saying: “Mold grows on cellulose.” They are referring to cellulose the generic material that forms the cell walls of all plants, not to cellulose insulation. Unfortunately, all too often this statement is taken to mean that cellulose insulation is exceptionally susceptible to mold contamination. In fact, due to its favorable moisture control characteristics and other factors associated with the manufacturing process relatively few cases of significant mold growth on cellulose insulation have been reported. All the widely publicized incidents of serious mold contamination of insulation have involved fiber insulation materials other than cellulose.
Moisture is always a concern for homes, and the wet-spray application of cellulose may not be a good choice in particularly wet climates unless the insulation. In very wet climates the use of a moisture meter will ensure proper installation and no possibility of mold issues. The dry-spray application is another option for very wet climates, allowing for a faster installation (though the wet-spray cellulose has an even higher R-value and can increase wall rigidity).
U.S. Health and Safety Partnership Program
In May 1999, the North American Insulation Manufacturers Association began implementing a comprehensive voluntary work practice partnership with the U.S. Occupational Safety and Health Administration (OSHA). The program, known as the Health and Safety Partnership Program, or HSPP, promotes the safe handling and use of insulation materials and incorporates education and training for the manufacture, fabrication, installation and removal of fiber glass, rock wool and slag wool insulation products. (See health effects of fiberglass). (For authoritative and definitive information on fiber glass and rock and slag wool insulation, as well as the HSPP, consult the North American Insulation Manufacturers Association (NAIMA) website (www.naima.org).)
^ | Home Energy Savings - Blown-In Cellulose Insulation
^ | US Department of Energy - Cellulose Insulation Material guide
^ Healthy House Institute, Fiberglass Insulation: Use With Care
U.S. Environmental Protection Agency and the U.S. Department of Energy's Office of Building Technologies.
Loose-Fill Insulations, DOE/GO-10095-060, FS 140, Energy Efficiency and Renewable Energy Clearinghouse (EREC), May 1995.
Insulation Fact Sheet, U.S. Department of Energy, update to be published 1996. Also available from EREC.
Lowe, Allen. "Insulation Update," The Southface Journal, 1995, No. 3. Southface Energy Institute, Atlanta, GA.
ICAA Directory of Professional Insulation Contractors, 1996, and A Plan to Stop Fluffing and Cheating of Loose-Fill Insulation in Attics, Insulation Contractors Association of America, 1321 Duke St., #303, Alexandria, VA 22314, (703)739-0356.
US DOE Consumer Energy Information.
Insulation Information for Nebraska Homeowners, NF 91-40.
Article in Daily Freeman, Thursday, 8 September 2005, Kingston, NY.
Alaska Science Forum, May 7 1981, Rigid Insulation, Article #484, by T. Neil Davis, provided as a public service by the Geophysical Institute, University of Alaska Fairbanks, in cooperation with the UAF research community.
Guide raisonné de la construction écologique (Guide to products /fabricants of green building materials mainly in France but also surrounding countries), Batir-Sain 2004