Spray foam insulation can be categorized into two types, which are open cell and closed cell expanding spray foam. Both open cell and closed cell foam are used as thermal insulation in homes and businesses, but they were designed for distinctly different applications.
Open cell foam is typically sold in a spray can, and although closed cell foam is usually sold in kit form, it is also available in a can for small projects. Open cell foam is usually used to seal up small cracks and gaps, while closed cell foam is used for larger projects.
Closed cell foam is also known as low-rise spray foam because it only expands about ⅓ as much as open cell foam. Closed cell spray foam is generally used to insulate an entire home, while open cell spray foam is more appropriate for small penetrations or gaps around framing.
Here we will discuss the similarities and differences between open cell and closed cell spray foam insulation and where each spray foam is typically used.
Open Cell Foam Basics
Open cell expanding spray foam is usually made from some form of elasticized rubber material, like polyisocyanate, or polyurethane. Typically, some form of inflating compound, like sodium bicarbonate is combined with the poly to form a sticky foam.
Open cell insulation foams are commonly used as thermal insulation and soundproofing, such as between a home theater and an adjacent bedroom. Open cell foam expands about three times as much as closed cell foam, so open cell foam is best for gaps exceeding 1” in width.
Thermal Efficiency ( R-Value)
Open cell foams have less insulation efficiency compared to closed cell foams, so you need more of it. Open cell spray foam provides about R-3 per inch, while closed cell provides closer to R-7 per inch.
Open cell foams are generally less expensive than closed cell foams by volume. However, as the popularity of both insulation foams increase, more options become available.
Open cell foam insulation varies in price from about $8.00 to $12.00 per can. Check the label to see how much area the can will cover. Open cell foams are semi-flexible and have higher thermal conductivity than closed cell foams.
As a result, open cell foam only provides about 50% of the R value of closed cell foam in the same quantity.
Open cell foam is recognizable from closed cell foam by its texture. Open cell foam is semi-flexible, so it should make a dent when you press on it. Closed cell foams are typically more rigid and stiff.
Where Is Open Cell Foam Preferable?
Those climatic regions where the temperature is higher and humidity is low, like the US southwest, open cell foam is preferred. Open cell foam is mostly used in hotter regions because the need for insulation is typically less than in more northern regions.
However, high temperature, high humidity regions are better served by closed cell foam because closed cell foam is much more resistant to moisture than open cell foam. The dense nature of closed cell foam provides little room for moisture, making closed cell foam more appropriate for coastal regions.
What Are the Pros and Cons Of Open Cell Spray Foam?
- Open cell foams are more flexible, so they move with natural materials, like wood, that expand and contract
- Open cell foam often costs less than closed cell foam
- Open cell foam doesn’t weigh as much by volume as closed cell foam, making open cell ideal when material weight is a consideration
- Open cell offers little resistance to moisture
- Open cell spray foam is less durable than closed cell foam because it is mostly air
- Open cell foam provides about 50% of the R value of closed cell foam by volume
- The chances of rot and mold growth are more likely because open cell foam will absorb water
Closed Cell Foam Basics
Closed cell foam creates small, distinct pockets of gas, with each one completely packed inside walls made of polymer. Closed cell foam is generally stiffer and more rigid than open cell foam, adding structural strength to the structure.
Closed cell foams create a number of encased air pockets, similar to rubber balls compacted inside a layer of elasticized rubber. When compacted, air releases through the cell wall and the air pockets are crushed down to small disc shapes. When the applied pressure is released, air enters again through the cell wall but at a slower rate, inflating the cell only slightly.
Thermal Efficiency ( R-Value)
Closed cell foam provides about twice the energy efficiency of open cell foam when installed at the same depth. The low expansion rate of closed cell foam allows the installer better control, so very little material is wasted.
Closed cell foam is often more expensive than open cell foam, as a square meter of closed cell foam generally costs between $8 and $25. Prices will vary, but closed cell foam in a comparable form (like a spray can), will typically cost about 50% more than open cell foam.
Closed cell foam can usually be identified by its color and/or texture. Closed cell foam is more dense than open cell foam, so pressing on it may not dent it. Closed cell foam is often blue or green, but check your closed cell foam kit for instructions.
When Is Closed Cell Foam Preferable?
Closed cell foam is a great choice when a high R value is required in a small space. Closed cell foam offers one of the highest R values by weight of any insulation material. Closed cell foam is available in both medium and high densities for specific applications.
Closed cell foam is also more hydrophobic than open cell foam. Although both foams prefer a dry surface, closed cell foam will usually perform better than open cell foam in a moist environment.
Is Closed Cell Foam Insulation Better Than Open Cell Foam?
One spray foam insulation isn’t necessarily better than the other. Both open cell foam and closed cell foam can be used on the same project, but often in different locations. Both closed cell foam and open cell foam prefer a dry, warm surface, but closed cell foam is more forgiving when conditions are not ideal.
What Are the Pros and Cons Of Closed Cell Spray Foam?
- High strength
- Longer useful life than open cell foam
- Closed cell foam is moisture and vapor resistant
- Has better soundproofing and thermal barrier ability than open cell
- Closed cell foam is twice as energy efficient as open cell foam
- Closed cell foam offers better rot and fungus protection because it offers better resistance to moisture than open cell foam
- Often more difficult to install compared to open cell foam
- Closed cell foam is often more expensive by volume than open cell foam
Checklist: Which One To Choose For Your Project, Open Cell Foam or Closed Cell Foam
Here are a few frequently asked questions and answers that can help you decide which type of cell foam, i.e. closed cell or open cell, is most appropriate for your project.
Q1) Which type of cell foam is more suitable for hotter regions to maintain a cooler temperature indoors?
Ans) Open cell foam is the most effective and suitable for cooling the inhouse temperature in hotter regions.
Q2) Which type of cell foam is best when providing extra strength to structural members is required?
Ans) Closed cell foam is used to provide extra strength to walls and roofs, as well as providing R value.
Q3) Which type of cell foam has a higher installation cost?
Ans) Closed cell foam is often 50% more expensive by weight than open cell foam.
Q4) Which cell foam is best against moisture and leakages in walls and roofs?
Ans) Closed cell foam provides better moisture resistance against vapors and leaks than open cell foam.
Q5) Which cell foam is preferred to insulate homes in extremely cold regions?
Ans) Closed cell foam is most effective for trapping the heat indoors due to its high insulation efficiency.
Q6) Which cell foam type is the better sound damper?
Ans) Closed cell foam is a better sound damper than open cell foam because the air pockets than carry sound are much smaller in closed cell foam.
Q7) For which type of houses, are open cell and closed cell foam effective?
Ans) Virtually any structure can be insulated with either open cell or closed cell foam because foam requires no adhesives or mechanical fasteners.
Q8) Which cell foam insulation has a higher efficiency and life service?
Ans) Closed cell foam has a higher insulation efficiency at about R-7 per inch, as compared to open cell foam which is R3.8 per inch.
Can You Mix Open Cell Foam And Closed Cell Foam?
You don’t want to literally use closed cell foam and open cell foam on the same spot at the same time. The foams are designed to expand at different rates, so mixing them will likely result in ruining the effectiveness of both.
However, you can mix closed cell foam and open cell foam once either has cured. For example, plumbers commonly seal pipe penetrations with open cell foam, even if the home will eventually receive whole house closed cell foam.
Why Is Closed Cell and Open Cell Foam Available In Different Weights?
When shopping for spray foam insulation options, you may encounter the same product in different weights. Spray foam insulation is graded by its density, or the weight of the foam in one cubic foot. More weight equals more density and generally better R value.
High Density (Closed Cell)
High density closed cell foam weighs about three (3) pounds per cubic foot. The minimum R value of high density foam is about 5.5, which also provides additional structural integrity.
Medium Density (Closed Cell)
Medium density closed cell foam weighs about two (2) pounds per cubic foot. Medium density is common in residential construction, as it offers a good balance of R value and cost.
Low Density (Open Cell)
Low density spray foam is also known as open cell foam. Low density foam expands about three times in size from initial application to fully cured. Open cell foam is good for closing small penetrations, as it expands around the opening as well.
Comparison: Which One To Choose For Your Project, Open Cell Foam or Closed Cell Foam?
Open Cell Foam
- Good for insulating around pipe and wire penetrations, or any gap 1” or smaller
- Generally the less expensive option, but you may need more of it than closed cell
- Easy to apply and requires no specific training, however you will need personal protective equipment
- Not preferred in humid locations
- Due to the expansion, open cell is not recommended around doors or windows
- Not as durable as closed cell foam, but both foams must be protected
Closed Cell Foam
- Closed cell foam is ideal when used as part of an energy conserving system, like a heat pump
- Offers both structural support and R value simultaneously in the high density form
- Offers excellent R value by volume, making closed cell foam ideal for walls, and ceiling whether they are framed or not
- About 50% more expensive than open cell foam
- Requires training in some versions, like a do-it-yourself kit
- If training is not available, professional installation is often the only other option
Summary: When Should You Choose Open Cell Foam
In most instances, open cell spray adhesive foam will offer the most benefits when applied to a small area. Open cell foam is perfect around pipe and wire penetrations, gas lines, and other openings 1” or smaller.
Open cell foam can be used in large areas, but because the foam offers about half of the R value of closed cell foam, the energy savings are smaller. Open cell foam used in a few small areas will reduce your overall energy costs by stopping drafts. Used on an entire home however, open cell foam will cost you about 50% of the effectiveness of your insulation.
The over expansion of open cell foam often results in an additional step, as the foam must be trimmed evenly with the surface. The foam trimmed away is wasted, so compared to closed cell foam, the more open cell foam you use, the more expensive the project becomes.
Summary: When Should You Choose Closed Cell Foam
Closed cell spray adhesive foam is often the best choice for whole house installations, as the expansion of the foam can be better controlled. Closed cell foams only expand to about double their initial size, so there is usually no over-expanded material to be trimmed away.
Because closed cell foam provides about R-7 insulation in a single inch, closed cell foam is ideal for 2” x 4” walls that require R-13 or higher. Closed cell foam can provide about R-23 in a 2” x 4” wall and R-40 in a 2” x 6” wall.