Spray foam (expanding foam in the UK) is a chemical product used in construction and engineering primarily as insulation and as a filler material. It is produced as a liquid but quickly expands and hardens into a stiff, lightweight structure. It is created by a chemical reaction of two component parts, commonly referred to as side A and side B. Side A contains very reactive chemicals known as isocyanate. Side B contains a polyol, which reacts with isocyanates to make polyurethane, and a mixture of other chemicals, including catalysts (which help the reaction to occur), flame retardant, blowing agents and surfactants. These react when mixed with each other and expand up to 30-60 times its liquid volume after it is sprayed in place. This expansion makes it useful as a specialty packing material which forms to the shape of the product being packaged and produces a high thermal insulating value with virtually no air infiltration.
History Otto Bayer (1902–1982) is credited with the invention of polyurethane in 1937. He succeeded in synthesizing polyurethane foam by exploring his basic idea that mixing small volumes of chemical substances could create dry foam materials. Polyurethane was further developed for different applications, ranging from shoe soles and cushions to industrial uses. In the 1940s rigid foam was applied to airplanes, and in 1979 polyurethane began being used as building insulation.
Properties
Thermal resistance R-value is the term given to thermal resistance to heat flow. The higher the R-value of an insulation product, the more effective the insulation properties. Spray polyurethane foam comes in a range of densities and cell structure. Low density foams are referred to as open cell SPF while higher density foams are referred to as closed cell foam. 1.8-2 pound polyurethane foam has the highest R-value of readily available spray foam insulation used in homes and buildings. Polyurethane is a closed-cell foam insulation material that initially contains a low-conductivity gas in its cells. As a result of the high thermal resistance of the gas, spray polyurethane insulation typically has an initial R-value around R-3.4 to R-6.7 per inch. In comparison, glass wool typically has an R-Value of only R-3 to R-4 per inch. Foam insulation blocks all three forms of heat transfer:
Conductive heat transfer The flow of thermal energy through a substance from a higher to a lower temperature region. Foam thermoset plastics reduce conductive heat transfer due in part to having very loose molecular bonds; In addition the cells of the installed spray foam are either filled with air in the case of open cell foam or HFCs (365mfc, 227ea, 245fa) or H(C)FOs (1336mzz(Z)), 1233zd(E)) in closed cell foam. Radiant heat transfer The process by which heat energy in the form of light (usually IR unless the substrate is hot enough to glow in the visible range) is emitted more strongly by warm surfaces and absorbed by other materials especially those of low IR reflectivity (think matte black finish). Radiant heat transfer does not require a medium. Foam insulation materials, such as spray foam insulation, are opaque to thermal radiation, like most solid materials. Convective heat transfer Heat which is created elsewhere that is transported by means of a fluid, such as water or in our case air. Spray foam insulation's most important attribute is the ability to air seal creating a custom airtight envelope within the building structure. The added benefit to air sealing is the ability to block convective heat transfer from interior to exterior during heating months and vice versa during cooling months, as the heat cannot escape through gaps in the buildings envelope without the aid of air movement from infiltration as a means of transport.
Applications
Packaging applications Spray foam is a very specialized packing material, often required for use in shipping valuable fragile items. Engineered packaging principles are designed to protect sculptures, vases, large fossils, lamp bases, busts, computers, furniture, chandeliers and other objects of unusual shape. By virtue of the liquid foam expanding by up to 30-60 times the volume of its liquid state, it efficiently protects almost any size, form and weight. The custom fit of the molds, top and bottom, securely and uniformly cushions the object. There are many types of alternative materials that can be used to handle more specific needs.
Building applications
Spray foam insulation or spray polyurethane foam (SPF) is an alternative to traditional building insulation such as fiberglass. A two-component mixture composed of isocyanate and polyol resin comes together at the tip of a gun, and forms an expanding foam that is sprayed onto roof tiles, concrete slabs, into wall cavities, or through holes drilled into a cavity of a finished wall. Closed-cell polyurethane (PU) foam is widely regarded as a versatile material and is employed in a range of applications beyond conventional wall and roof insulation. It is commonly used to insulate roofs, floors, windows, and walls, as well as containers, boats, crawl spaces, and basements. In addition to providing thermal resistance, it can help to prevent condensation on windows and walls, reduce noise transmission by filling hollow spaces, and minimise thermal bridging. Owing to its dense structure, closed-cell PU foam is also frequently applied to seal cracks and construction joints, contributing both to air tightness and structural integrity. "Spray foam" is also an informal term used to refer to various plastic foam materials that are used in building construction to provide thermal insulation and minimize air infiltration. Polyurethane and polyisocyanurate are two types of foam used in this application.
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