Closed Cell vs Open Cell Foam Insulation
Before we can go into that we need to start by saying that in the foam insulation industry there are usually two types of foam insulation being used, open-cell and closed-cell.
There are several major differences between the two types, leading to advantages and disadvantages for both, depending on the desired application requirements.
In addition, polyurethane spray foam is an extremely versatile material that is available in a variety of final physical properties and densities, so it is necessary for the end-user to have an understanding of these differences, and to choose the spray foam system that is best suited for the particular application requirements.
Both types of foam are commonly used in most building applications. Some are inappropriate in specific applications. For example, you typically would not use open-cell foam below grade where it could absorb water; this would negate its thermal performance because water is a poor insulator compared to air.
Closed-cell foam would be a good choice where small framing sizes need the greatest R-value per inch possible. Basically, the choice depends on the conditions of each installation. We routinely select from a wide variety of foam systems with varying characteristics, depending on the particular requirements of our clients’ projects.
Closed-cell polyurethane spray foam is among the most efficient insulating materials commercially available, with Aged R-values commonly around 6.7 per inch and LTTR values between 5.2 – 5.6.
Closed-cell foam incorporates an insulating gas that is retained within the cells (foam “blowing agent”), which leads to the highly efficient insulating properties of the material. In the U.S., insulation is measured in “R-Value” (R= resistance to heat flow), in Canada now, it is measured in LTTR (Long Term Thermal Resistance) and closed-cell polyurethane spray foam has among the highest R-Values of any commercially available insulation.
In addition, the closed-cell nature of this foam provides for a highly effective air barrier, low moisture vapour permeability (often referred to as the “Perm” rating), and excellent resistance to water. The most common foam density for closed-cell polyurethane foam is approximately 2.0 pounds per cubic feet.
Years of research and commercial experience has shown that the 1.9 – 2.5 lb./ft3 density range provides the optimum insulating and strength characteristics for most building applications. Closed-cell polyurethane foams are usually characterized by their rigidity and strength, in addition to the high R-Value. 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, since foam density is directly related to yield (lower density = higher yield). Although the R-value of open-cell foams is slightly more than 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 vapour, with perm ratings of approximately 10.0 per 4 – 5 inches thickness (up to 50 perms at one inch). However, the foam allows for a very controlled diffusion of moisture vapour whose consistency can be managed by the builder/architect.
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.
Applications that typically use open-cell foam include residential construction insulation and for sound deadening in media rooms, etc. Closed-cell foam, while also useful in residential construction insulation, is used in a variety of commercial, industrial and residential applications because of the excellent strength and insulating properties described here.