CLOSED CELL INSULATION

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APPLICATION: Under slabs; walls, ceilings, roofs, foundations, attic, crawl spaces, floors, piping

Closed-cell spray foams provide a higher R-value per inch than less expensive insulation types like fiberglass, cellulose, or open-cell foam.

Closed-cell spray foam is the most expensive residential insulation. When installed well, however, it performs better than any other insulation. It's a great air barrier, is invulnerable to moisture, and it's an effective vapor retarder. Because of its density and gluelike resolution, it also adds structural strength to a wall, ceiling, or roof. To seal air leaks in retrofit applications as well as new construction—for example, at rim joists or the attic side of partition top plates—closed-cell spray foam is an very practical material.

Many green builders will avoid the use of closed-cell spray foam because the blowing agents in most types of closed-cell spray polyurethane foam are hydrofluorocarbons (HFCs) with a high global-warming potential.

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OPEN CELL INSULATION

APPLICATION: Walls, ceilings, roofs, attics

The low density of open-cell foam makes it fairly vapor permeable, so when it’s used to create an unvented conditioned attic in a cold climate, the interior face of the foam should be covered with a vapor retarder. This can be accomplished by spraying the cured foam with vapor-retarding paint.

Open-cell foams use water or carbon dioxide as the blowing agent. Some open-cell foams are made partly from bio-based raw materials—for example, soybean oils—in place of a portion of the petrochemicals. Like closed-cell foam, open-cell foam creates an efficient air barrier.

Unlike closed-cell foam, however, open-cell foam absorbs and holds water, has a lower R-value per inch, and is vapor permeable. The permeable nature of open-cell foam can be a plus or minus, depending on the application.