For large to mid scale applications, a two component mixture comes together at the tip of a gun, and forms an expanding foam that is sprayed 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.
Blocks airflow by expanding and sealing off leaks, gaps and penetrations.
Can serve as a semi-permeable vapor barrier with a better permeability rating than plastic sheeting vapor barriers and consequently reduce the build up of moisture, which can cause mold growth.
Can fill wall cavities in finished walls without tearing the walls apart (as required with batts).
Works well in tight spaces (like loose-fill, but superior).
Provides acoustical insulation (like loose-fill, but superior).
Expands while curing, filling bypasses, and providing excellent resistance to air infiltration (unlike batts and blankets, which can leave bypasses and air pockets, and superior to some types of loose-fill. Wet-spray cellulose is comparable.).
Increases structural stability (unlike loose-fill, similar to wet-spray cellulose).
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 of all, with the exception of cementitious foams, release toxic fumes when they burn.
According to the U.S. Environmental Protection Agency, there is insufficient data to accurately assess the potential for exposures to the toxic and environmentally harmful isocyanates which constitute 50% of the foam material.
Depending 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.
Can shrink slightly while curing if not applied on a substrate heated to manufacturer's recommended temperature.
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.
Many foam insulations are made from petrochemicals and may be a concern for those seeking to reduce the use of fossil fuels and oil. However, some foams are becoming available that are made from renewable or recycled sources.
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.
If one does not wear a protective mask or goggles, it is possible to temporarily impair one's vision. (2–5 days)
Advantages of closed-cell over open-cell foams
Open-cell foam is porous, allowing water vapor and liquid water to penetrate the insulation. Closed-cell foam is non-porous, and not moisture-penetrable, thereby effectively forming a SEMI-permeable vapor barrier. (N.b., vapor barriers are usually required by the Building Codes, regardless of the type of insulation used. Check with the local authorities to find out the requirements for your area.)
Closed-cell foams are superior insulators. While open-cell foams typically have R-values of 3 to 4 per inch (RSI-0.53 to RSI-0.70 per inch), closed-cell foams can attain R-values of 5 to 8 per inch (RSI-0.88 to RSI-1.41 per inch). This is important if space is limited, because it allows a thinner layer of insulation to be used. For example, a 1-inch layer of closed-cell foam provides about the same insulation factor as 2 inches of open-cell foam.
Closed-cell foam is very strong, and structurally reinforces the insulated surface. By contrast, open-cell foam is soft when cured, with little structural strength.
Open-cell foam requires trimming after installation, and disposal of the waste material. Unlike open-cell foam, closed-cell foam rarely requires any trimming, with little or no waste.
Icynene spray formula
R-3.6 (RSI-0.63) 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. 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 many post-industrial countries.
Sealection 500 spray foam
R-3.8 (RSI-0.67) per inch. a water-blown low density spray polyurethane foam that 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.
One example is Air-Krete R-3.9 (RSI-0.69) per inch. Non-hazardous. Is the only foam not restricted to a depth of application. Being fireproof, it will not smoke at all upon direct contact with flame, and is a two-hour firewall at a 3.5 in (89 mm) (or normal 2 × 4 in (51 × 100 mm) stud wall) application, per ASTM E-814 testing (UL 1479). 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 cement and air, which is 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: Fragile at the low densities needed to achieve the quoted R value and, like all foams, it is more expensive than conventional fiber insulations.
Typically R-5.6 (RSI-0.99) or slightly better after stabilization - higher values (at least R-7, or RSI-1.23) in stabilized boards. Less flammable than polyurethane.
Phenolic injection foam
Such as Tripolymer R-5.1 per inch (ASTM-C-177). Known for its air sealing abilities. Tripolymer can be installed in wall cavities that have fiberglass and cellulose in them. Non-hazardous. Not restricted by depth of application. Fire resistant – flame spread 5, smoke spread 0 (ASTM-E-84) - will not smoke at all upon direct contact with flame and is a two-hour firewall at a 3.5 in (89 mm), or normal 2 × 4 in (51 × 100 mm) stud wall, application per ASTM E-199. Great for sound deadening, STC 53 (ASTM E413-73; does not echo like other foams. Environmentally friendly. Non-expansive (good for existing homes where interior sheathing is in place). Fully sustainable: Consists of phenolic, a foaming agent, and air. 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: Like all foams, it is more expensive than conventional fiber insulations when only comparing sq ft pricing. When you compare price to R value per sq ft the price is about the same.
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.
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 someone 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
An HFC used in some closed-cell spray foam insulations. Although it has zero ozone depletion potential, it has a high global warming potential of 950 (meaning it is 950 times as potent as CO2 in its global warming effect). For example, E:zero spray foam solutions offers both open and closed cell varieties of spray foam insulation, some of which use Enovate high global warming potential blowing agents.