• Expanding foam insulation applied with a spray is an effective, durable and common means of insulating. Because the foam expands to fill any given area, there are no gaps as with other forms of insulation which must be cut to size. The tight seal of foam insulation avoids excess conduction and improves energy efficiency. In addition, expanding foam insulation is more practical to install in cramped or hard-to-reach locations. Several kinds of spray foam insulation are available, though polyurethane foams are the most predominant material.
  
  

Polyurethane Foam

• Polyurethane foam has the highest R-value of any residential insulation material, a rating which means that it can insulate against temperature change more effectively than any other material. At a 6.2 R-value, it has nearly two times the insulating capacity of fiberglass, making it an excellent option for energy-efficient building. According to North Carolina Foam Industries' Roger Morrison, builders in warmer locations tend to combine spray-applied polyurethane foam with glass fiber batt. They cover a 1/2-inch thick layer of spray foam with an additional layer of glass fiber batt. The spray foam both serves as an air barrier and increases the total R value. In colder climates, many builders completely fill walls with foam, achieving a higher overall R value.
  
  

HCFC-Combined Insulation

• Originally, spray foam insulations contained chlorofluorocarbons (CFCs) to produce the foaming effect. With increased awareness of CFC's harmful effects on the ozone, all insulation now uses non-CFC components. Some varieties combine with an HCFC gas to avoid damaging the ozone layer but to achieve an effect approaching that of CFC-combined insulation. Hydrochlorofluorocarbons (HCFCs) are insulation materials that have replaced CFCs; unlike their predecessors, they have low toxicity levels. While the insulation combined with HCFC gas is not as effective as that with CFCs, the insulation still has a relatively high R factor, of 6.5. HCFC-based insulation has a density around two pounds per cubic foot, with low-density foams getting as low as .5 pounds per cubic foot.
  
  

UFFIs

• Discontinued since the 1980s, urea formaldehyde foam insulation (UFFI) once served as efficient spray foam insulation until the discovery of deleterious formaldehyde vapors interrupted its popularity. The high formaldehyde levels came from poor mixing and application practices as well as variation among human sensitivity. Although the Consumer Product Safety Commission's ban on UFFIs was overturned, granted that properly-mixed products did not necessarily cause any harm, the material's publicity had already alienated the public. Should you discover an older home has UFFI in its walls, you may test the air for formaldehyde levels. Some trace levels of formaldehyde are normal, derived from common materials like plywood or particle board.