The Differences Between Open Cell and Closed Cell Polyurethane Spray Foam

Polyurethane spray foam is a widely used and widely accepted method of providing insulation for a broad range of applications, from refrigerator interiors to attic crawlspaces. The benefits of a spray foam, as opposed to other types of insulation, include quick application, dexterity in hard to read spots and generally robust resistance to diverse environmental conditions.

There are two primary types of polyurethane spray foams, known as open cell and closed cell. They differ in densities and other aspects that can be beneficial or detrimental in a given application.

Closed Cell Polyurethane Spray Foam

Closed cell is the denser and more common of the two types of Spray Foam Insulation. The common measurement system for foam resistance to heat flow (i.e., insulation) is a foam’s “R-Value.” Closed cell polyurethane foams have higher R-values than other types of foam, around 6.0 per inch, although some stronger ones have R-values of 7.14 per inch and higher. Closed cell foams feature better insulation because of this resistance, and are also more resistant to water degradation or penetration, which includes moisture build-up. Moisture can eventually attract bacterial growth, promoting mold, which can eat away at wood and compromise structural integrity. Preventing moisture migration can help greatly curb mold growth.

Closed cell foams are also dense enough to insulate air, preventing drafts and keeping in regulated temperatures. This density also prevents mold growth because temperature control can cut down on humidity, which spawns mold. In order to maintain their resistance, closed cell foams are usually dense and strong, and resemble solids when they fully form. This strength not only helps to insulate buildings and appliances, but can also strengthen walls to which it is applied.

Open Cell Polyurethane Spray Foam

Open cell polyurethane spray foams are much less common because they were originally manufactured by only one company, and their R-values are much fewer than those of closed cell sprays. However, as their strengths were discovered, other companies began using them. Installation is similar to that of closed cells, but the effects are different. Open cell foam sprays expand once applied, allowing them to be installed in hard to reach, out of the way nooks and crannies. This includes wall and ceiling cavities that can be difficult to seal with closed cell foams. The expansion feature will hermetically seal the area and provide proper insulation. However, the R-value of open cell polyurethane spray foam is lower, in the 3.6 to 3.8 per inch range. This means its heat resistance level is lower, which can cause insulation failures in extreme temperatures. Because open cell foam is still very dense, it provides good insulation. Open cell spray foam does not have water resistance, though, and its lower strength provides less support to walls. It is also more permeable to vapor and air, and lower noise frequency ranges.

Another positive attribute of open cell polyurethane foam is its cost. Because of its disadvantages compared to closed cell foam spray, it is more affordable. This can be a great boon when an application does not require airtight seals and hermetic moisture prevention. Caution needs to be taken, though, that the less expensive alternative does not lead to more expensive repairs in the future. Establishing the needs of a given application are important before choosing which foam spray to use.

If you are considering spray foam insulation, call the experts at Superior Insulation Services at 860.238.3113 or visit us online at

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