NEWS Environmental Building News (January 2009) Features What's Happening Product News & Reviews BackPage Primers Opinion GreenSource Magazine EBN Archives

Foam-in-Place Polyurethane Insulation

Among the many insulation materials we can choose from are foam-in-place products for filling cavities or creating a continuous layer on a wall or roof system. The most common of these is spray polyurethane foam, referred to in the industry as SPF.

There are two types of polyurethane foam: closed-cell and open-cell, both of which must be installed by trained insulation contractors.

Closed-cell, high-density polyurethane has been around for decades, but it has changed considerably in the past 15 years as ozone-depleting CFCs were replaced first with HCFCs and, more recently, with an ozone-safe HFC. The two-part foam is sprayed as a liquid, much like spray paint, and as the two components (a polyol resin and an isocyanate) mix, a chemical reaction occurs causing the foam to quickly expand 20- to 30-fold, forming the insulation. In a few hours the material cures to form a fairly hard insulation with a density of about two pounds per cubic foot (32 kg/m³). Closed-cell polyurethane insulates to between R-5.8 and R-6.8 per inch—considerably higher than any other cavity-fill option—and adheres tightly to wood and other materials, forming an excellent air barrier. In some parts of the country, closed-cell polyurethane is used as an exterior insulated roofing that is finished with a durable, UV-resistant elastomeric coating.

Open-cell, low-density polyurethane was pioneered by the Canadian company Icynene but is now made by several manufacturers. The foam is installed into wall and ceiling cavities in a similar fashion as closed-cell foam, except that the material expands 100- to 150-fold. Installers usually spray enough foam to fill or slightly overfill the cavity, and then use a specialized tool to shave the foam flush with the inner face of the framing. The cured foam has a density of about a half-pound per cubic foot (8 kg/m³), so it uses a lot less material than closed-cell foam. The material insulates to between R-3.6 and R-3.8 per inch, provides a good air barrier, and has always been ozone-safe. Open-cell polyurethane has to be enclosed in a cavity because it remains fairly soft. Despite its lower insulation value per inch, the overall energy performance in a wall or ceiling cavity is generally comparable to that of closed-cell polyurethane because open-cell polyurethane is usually installed to fill the cavity while closed-cell polyurethane is installed in a thinner layer. Open-cell polyurethane is also available in a more slowly expanding formulation that can be poured into a wall cavity—so it can be used for retrofitting uninsulated walls in existing buildings.

Several manufacturers offer biobased formulations of spray polyurethane foam in which a portion of the polyol component is derived from soybean oil rather than petroleum hydrocarbons. Biobased materials are attractive environmentally because they are renewable, but the environmental impacts of agriculture can be significant, and biobased materials have come under criticism for contributing to rising food prices.

---

Reader-contributed comments related to EBN: 17:10 - Foam-in-Place Polyurethane Insulation. Comments are listed with newest at the top.

Log in to add comments - Help with comments

---

---

IMAGE CREDITS:
1. Illustration: Amie Walter

DISCUSSIONS Performance of SPF Jamie Wolf Nov 11, 2008 More comments RELATED GREEN DESIGN Wall Insulation RELATED CSI LISTINGS Sprayed Insulation CSI Section 07 21 29