Polyurethane spray foam is a versatile insulation material that is sprayed into building cavities where it quickly expands and molds itself to its surroundings. It is available in “closed-cell” and “open-cell” varieties, each of which offers advantages and disadvantages, depending on the requirements of its application. The following guide briefly explains the differences between these insulation options.
Closed-Cell Polyurethane Foam
Closed-cell polyurethane foam is composed of tiny cells with solid, unbroken cell walls that resemble inflated balloons piled tightly together. The cells are inflated with a special gas selected to make the insulation value of the foam as high as possible. Wall-racking strength can by enhanced when closed-cell foam is applied, and its strength makes it preferable for roofing applications. The high thermal resistance of the this foam is significantly better than its open-cell alternative. It also acts as a vapor barrier, making it the product of choice if the insulation is likely to be exposed to high levels of moisture. Its density is generally 30-40 kilograms per cubic meter [kg/m3].
Open-Cell Polyurethane Foam
Open-cell polyurethane foam is a soft, flexible, spongy insulation with broken cell walls that permit air to fill them. They typically have a density of 8-12 kilograms per cubic meter [kg/m3], which is significantly less than closed-cell insulation, as well as having a reduced R-value per inch, although these foams still have excellent thermal-insulating and air-barrier properties. The foam is weaker and less rigid than closed-cell foams, too. It will require trimming and disposal of excess material as it expands to over 100 times its initial liquid size. Builders often choose open-cell foam for the following advantages it affords, including:
- its low cost. Where economical yield is important, open-cell foam is generally chosen over its more cost alternative;
- providing a sound barrier. This forms a more effective sound barrier in normal-frequency ranges than closed-cell foam. For this reason, these foams are well-suited for installation beneath floors and around theater rooms;
- its flexibility. Open-cell foam is more flexible than closed-cell foam, which allows it to adjust to weather-induced expansion and contraction of framing members. Open-cell foam, by contrast, may develop hairline fractures because it cannot flex sufficiently; and
- its permeability to moisture. While often cited as a reason to avoid the use of foam, in certain situations, it can be helpful for moisture to pass through insulation. Open-cell foam used in roofs, for instance, will allow a roof leak to make its way to the space below where it is more likely to be discovered. Closed-cell foam used in the same application would trap the moisture, hiding the leak and potentially leading to wood decay. In most situations, however, Open-cell foam should not be used in any place where it might become wet, as moisture will diminish its insulative value.
In summary, polyurethane foam is available in two varieties that are suited for different 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 in into a cavity of a finished wall.
“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 (PUR) and polyisocyanurate (PIR) are two types of foam used in this application.
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.