Open Cell Vs. Closed Cell Spray Foam Insulation

Foam insulation–rigid or spray–comes in two types: open cell or closed cell. Both insulate a home, but they have different R-values, applications, and costs.

Open cell vs closed cell insulation spray foam

What is Closed Cell Foam?

Manufacturers create closed-cell foam by introducing a blowing agent into the chemical reaction used to make polyurethane. The process creates tiny pockets of gas in the finished product. Each pocket is completely enclosed by the polymer–giving the foam product its name.

Most insulation materials depend on dead air spaces to prevent heat conduction – even fiberglass blanket insulation and cellulose blown-in insulation. The products themselves are not the insulator; they trap and hold air (which is a gas) to do the job. Polyurethane foam works the same way. Closed cell foam insulation–both rigid and sprayed–is efficient at trapping air pockets. It has R-values of R-5.0 or higher.

Benefits of Closed Cell Foam

Some of the benefits of closed cell foam vs. open cell foam.


Moisture cannot penetrate closed-cell foam. It provides its own semi-permeable vapor barrier when it is a minimum of 2” thick and gaps and holes are sealed.

Closed-cell spray foam can perform better than poly vapor barriers.

Superior Insulation Value

Closed-cell foam insulation boasts an R-value of R-5.0 per inch to R-8.0. Its high R-value is helpful when space is limited. For example, two inches of closed-cell rigid foam glued to concrete basement walls provides the same R-value as a framed 2 x 4 stud wall with fiberglass batt insulation.

Excellent Strength

Closed-cell foam insulation is strong enough to structurally reinforce the insulated surfaces. It also fills gaps, cracks, and holes, helping to hold the structure together. Windows and doors will not move if foamed in place–even without fasteners.

Low Expansion

Almost all closed-cell spray foam insulation has little or no expansion after application, which means installers don’t have to trim it–saving time, material, and cost. It does not warp or pressure surrounding material such as window and door frames, plumbing, heating, and electrical components.

Disadvantages of Closed Cell Foam

As attractive as closed-cell foam insulation is, it’s not a good fit for all applications.

May Seal Too Well

In-home construction, wood is considered dry at 19% moisture content. It will continue drying after the house is framed–eventually stabilizing at 8% – 14%. If framing members are completely sealed with closed cell foam, drying out cannot occur.

Poor Sound Barrier

Closed cell foam–especially spray foam–is a poor soundproofing material. It will not absorb sound waves. Also, because it adheres to the wall, low-frequency bass sound waves will vibrate and pulse with the sound energy and pass through the wall unchanged.

More Expensive

Closed-cell foam does not expand as much as open-cell foam. It requires two or three times as much to insulate the same area.

What is Open Cell Foam?

Manufacturers use a different blowing agent to make open-cell foam, which causes some or all of the gas pockets to expand and open. A foam product is an open cell if half or more of the gas pockets are open.

Open-cell foam is a softer, more malleable product. As insulation, it’s best where a little airflow is wanted or needed. Manufacturers also use it in furniture and vehicle upholstery, mattresses, packaging material, and bath sponges.

Benefits of Open Cell Foam

Open cell foams have an R-value of around R-3.5 per inch–almost the same as fiberglass batt insulation. Using open-cell spray foam insulation in stud cavities provides the same R-value as blanket insulation. It has the added benefit of sealing gaps, cracks, and holes and providing better soundproofing.

Allows Framing Members to “Breathe”

Wood is a hygroscopic material, meaning it absorbs moisture or dries out to help balance its surrounding environment. Open cell foam allows the wood to breathe moisture in and out without trapping it inside.

Better Soundproofing Product

Mass and absorption are two of the mainstays of sound attenuation. Open-cell foam is twice as good at soundproofing as closed-cell foam because it absorbs and dissipates sound waves. It’s so good that manufacturers use it in soft sound-absorbing acoustic panels.

High Expansion Product

Open-cell spray foam expands up to two or three times its original size, filling in holes, gaps, and large cavities. The amount of expansion helps to insulate hard-to-reach areas, making it more economical than closed-cell foam.

Disadvantages of Open Cell vs. Closed Cell Spray Foam

Open-cell foam is much less expensive but also provides about half the R-value of closed-cell foam. Here are some other disadvantages of open-cell vs. closed-cell spray foam.

Porous Material

Open-cell foam is porous. Water vapor from humidity can absorb into the open cells.

Open cell foam doesn’t act as a vapor barrier, and the moisture inside the product can provide a growing medium for mold and mildew.

If open-cell foam absorbs moisture and freezes, the cells and polyurethane can damage due to the expansion of the ice particles.

Lower Insulation Value

Open-cell foam insulation has half the R-value of closed-cell foam. It’s not the best product where space is at a premium. More extreme climates–cold or hot–require more and better insulation.

High Expansion and Slow Curing

Open cell foam expands up to 3 times its applied size. As beneficial as this can be in some situations, it can also warp window and door frames and stress plumbing, electrical and venting. Open-cell spray foam also takes longer to cure. Working with a product that continues to expand extends project completion times.