Home insulation techniques have evolved dramatically from the days of just pink fiberglass rolls of insulation. Today, the leading home builders are leveraging spray foam technology. Spray foam offers much better thermal resistance and energy efficiency. While there are many variations of spray foam, there are two primary types to consider: open-cell and closed-cell foam.
In comparing open-cell versus closed-cell foam, there are a couple of key factors to consider. The first is the physical structure or chemical composition of each. Open-cell foam, as the name indicates, is literally tiny foam cells that are not completely closed. The small openings in each cell allow air to fill and expand the foam. This creates a softer, lighter, weaker, and less thermal resistance foam.
Closed-cell foam differs in that all of its miniature foam cells are closed and tightly packed together. Furthermore, the cells are filled with a gas (foam “blowing agent”) that helps the foam rise, expand, and become a highly efficient insulator. These cells can be formulated to obtain many characteristics, the most common being size and density.
The density of spray foam is measured by weighing one cubic foot of material. Open-cell foams typically weigh 0.4 to as much as 1.2 lbs/ft3. Closed-cell foam for insulation purposes rand in density from 1.7 lbs/ft3 to 2.0 lbs/ft3. Roofing applications typically use a 2.8 to 3.0+ lbs/ft3. to support traffic and loads better. The higher the density the foam, the heavier, or stronger it becomes.
Closed-cell polyurethane spray foam is among the most efficient insulating materials commercially available, with R-values (R= resistance to heat flow) commonly around 6.0 per inch. In addition, the closed-cell nature of this foam provides for a highly effective air barrier, low moisture vapor permeability (often referred to as the “Perm” rating), and excellent resistance to water. Also, studies show that wall racking strength can by doubled or tripled when closed cell foam is applied.
Open-cell polyurethane spray foam, on the other hand, is usually found in densities ranging from 0.4 to 1.2 lbs/ft3. One of the advantages that these lower densities provide is a more economical yield. Although the R-value of open-cell foams is roughly half that of closed-cell foams, usually around 3.5 per inch, these products can still provide excellent thermal insulating and air barrier properties. Open cell foam is more permeable to moisture vapor, with perm ratings of approximately 16 per 3 inches thickness (up to 30-35 perms at one inch). However, the foam allows for a very controlled diffusion of moisture vapor whose consistency can be managed by the builder / architect. Open Cell foam is not recommended for use in exterior applications, or applications where it can be in direct contact with water. Open cell foams are incredibly effective as a sound barrier, having about twice the sound resistance in normal frequency ranges as closed-cell foam. Other characteristics of open-cell polyurethane foam usually include a softer, “spongier” appearance, as well as lower strength and rigidity than closed-cell foams.