When choosing spray foam insulation, one of the first decisions you'll need to make is whether open-cell or closed-cell spray foam is right for your project.
Both types of spray foam insulation can help improve a building's energy efficiency and reduce unwanted air movement, but they have important differences in density, structure, R-value, moisture resistance, expansion, and typical applications.
So, which one should you choose?
In this guide, we'll compare open-cell vs. closed-cell spray foam insulation and explain the key differences to help you make a more informed decision.
What Is Spray Foam Insulation?
Spray foam insulation is a polyurethane insulation material that is applied as a liquid and expands to fill gaps, cracks, and cavities. Once cured, it creates an insulating layer that can also help reduce air leakage.
Spray foam is commonly used in:
- Attics
- Roof assemblies
- Walls
- Crawl spaces
- Rim joists
- Around suitable penetrations and gaps
- Other areas where air sealing and insulation are needed
The two main types are open-cell spray foam and closed-cell spray foam.
While they may look similar after installation, their physical properties and performance can be quite different.
Open-Cell vs. Closed-Cell Spray Foam: What's the Difference?
The biggest difference is the structure of the foam cells.
Open-Cell Spray Foam
Open-cell foam contains cells that are not completely sealed. This gives the foam a softer, lighter, and more flexible structure.
It typically expands more than closed-cell foam and can be useful for filling larger cavities where a thicker layer of insulation can be installed.
Closed-Cell Spray Foam
Closed-cell foam has a much denser structure, with the majority of its cells fully enclosed.
This makes it more rigid and gives it a higher R-value per inch compared with open-cell foam.
Closed-cell foam is often chosen when space is limited and higher insulation performance per inch is desired.
Open-Cell vs. Closed-Cell Spray Foam Comparison
| Feature | Open-Cell Foam | Closed-Cell Foam |
|---|---|---|
| Cell structure | Open | Closed |
| Density | Lower | Higher |
| Texture | Softer | More rigid |
| Expansion | Higher | Lower |
| R-value per inch | Lower | Higher |
| Moisture resistance | Lower | Higher |
| Air sealing | Yes | Yes |
| Insulation performance per inch | Lower | Higher |
| Typical use | Large cavities, attics, walls | Walls, crawl spaces, roofs, tighter spaces |
The right choice ultimately depends on the location, available space, climate, moisture exposure, and the goals of your insulation project.
What Is Open-Cell Spray Foam?
Open-cell spray foam is a lightweight insulation material with a cellular structure that allows the cells to remain partially open.
Because of its lower density, open-cell foam is generally softer and expands significantly during installation.
This makes it useful for filling large cavities and creating an air barrier where sufficient installation space is available.
Advantages of Open-Cell Spray Foam
More expansion
Open-cell foam expands significantly after application, allowing it to fill larger cavities.
Lightweight
Its lower density makes it lighter than closed-cell foam.
Flexible
The softer structure can make it suitable for certain interior applications where flexibility is beneficial.
Good for larger cavities
Open-cell foam can be useful when there is plenty of space for a thicker insulation layer.
Limitations
The lower density also means open-cell foam generally provides less insulation per inch than closed-cell foam.
It is also more permeable to moisture and water vapor, making application location particularly important.
What Is Closed-Cell Spray Foam?
Closed-cell spray foam has a dense cellular structure in which the individual cells are largely sealed.
This gives the foam its characteristic rigid texture and allows it to provide a higher level of insulation per inch.
For projects where available space is limited, closed-cell foam can be particularly useful because you can achieve more insulation performance without requiring as much thickness.
Advantages of Closed-Cell Spray Foam
Higher R-value per inch
Closed-cell foam generally provides more insulation performance per inch than open-cell foam.
Dense and rigid
The cured foam creates a firm insulation layer.
Excellent air sealing
Closed-cell foam can help seal gaps, cracks, and penetrations where air leakage is a concern.
Lower moisture permeability
Its closed-cell structure makes it less permeable to moisture than open-cell foam.
Useful where space is limited
Because it provides higher insulation performance per inch, it can be a practical choice for tighter spaces.
Which Has a Higher R-Value?
One of the biggest differences between the two types is insulation performance per inch.
In general, closed-cell spray foam has a higher R-value per inch than open-cell spray foam.
R-value measures how well an insulation material resists heat flow. A higher R-value generally means greater resistance to heat transfer.
However, R-value isn't the only factor to consider.
The overall performance of an insulation system can also depend on:
- Installation thickness
- Coverage
- Air leakage
- Moisture conditions
- Installation quality
- Building design
- Climate
For this reason, choosing insulation shouldn't be based solely on the R-value printed on the product.
Open-Cell vs. Closed-Cell: Which Is Better for Moisture?
Closed-cell foam generally provides greater resistance to moisture because of its dense, closed cellular structure.
This can make it advantageous in areas where moisture exposure is a concern.
However, spray foam should not be treated as a universal waterproofing solution. The suitability of a particular foam product depends on the application, substrate, building assembly, and manufacturer's specifications.
If you're insulating an area that regularly experiences water intrusion, the underlying moisture problem should be addressed before installing insulation.
Which Spray Foam Is Better for Air Sealing?
Both open-cell and closed-cell spray foam can help reduce unwanted air movement when properly installed.
This is one of the major advantages of spray foam insulation compared with traditional insulation materials that may not create the same level of continuous air sealing.
For example, spray foam can be used around suitable:
- Gaps
- Cracks
- Joints
- Utility penetrations
- Framing connections
The key is proper surface preparation and application.
When Should You Choose Closed-Cell Spray Foam?
Closed-cell foam may be a good option when:
- You need higher insulation performance per inch
- Available installation space is limited
- You want a denser insulation material
- Moisture resistance is an important consideration
- You need to seal irregular gaps and penetrations
- You're working in a crawl space or similar area where conditions require a more moisture-resistant insulation material
It is especially useful in situations where adding several inches of insulation isn't practical.
When Should You Choose Open-Cell Spray Foam?
Open-cell foam may make sense when:
- There is plenty of space for thicker insulation
- A lightweight insulation material is preferred
- You're insulating large cavities
- The application is appropriate for a more moisture-permeable foam
However, always consider the specific building assembly and local requirements before choosing an insulation type.
Is Closed-Cell Spray Foam More Expensive?
Generally, closed-cell spray foam costs more per board foot than open-cell foam because it uses more material and has a higher density.
However, comparing price alone can be misleading.
Because closed-cell foam provides more insulation performance per inch, you may need less thickness to achieve a particular insulation target.
When comparing products, consider the cost per unit of insulation performance, not just the price of the individual can or kit.
Can You Install Spray Foam Yourself?
Yes, certain spray foam products are designed for DIY applications.
Small projects such as sealing appropriate gaps, cracks, penetrations, and other accessible areas may be manageable for homeowners with the right equipment and preparation.
However, larger insulation projects require more planning.
Before starting a DIY spray foam insulation project:
- Read the manufacturer's instructions.
- Check the recommended application temperature.
- Prepare the surface properly.
- Wear the required PPE.
- Ensure adequate ventilation.
- Apply the foam according to the recommended thickness and technique.
- Allow sufficient curing time.
For large or complex projects, professional installation may be the better choice.
How to Choose Between Open-Cell and Closed-Cell Spray Foam
Instead of asking "Which spray foam is better?", it's more useful to ask:
"Which spray foam is better for my specific application?"
Consider these five factors:
1. Available Space
If you have limited space, closed-cell foam's higher R-value per inch can be advantageous.
2. Moisture Exposure
If the area may experience moisture, closed-cell foam may be more appropriate, depending on the complete building assembly.
3. Desired Insulation Performance
If you want more insulation performance from a thinner layer, closed-cell foam is generally the stronger choice.
4. Project Location
An attic, wall cavity, crawl space, rim joist, and exterior application may have different requirements.
5. Budget
Open-cell foam can be less expensive per board foot, while closed-cell foam can provide greater insulation performance per inch.
Open-Cell vs. Closed-Cell Spray Foam: The Bottom Line
Both types of spray foam insulation have their place.
Open-cell spray foam is lightweight, softer, and highly expansive, making it useful for certain large cavities where sufficient space is available.
Closed-cell spray foam is denser, more rigid, and provides higher insulation performance per inch, making it a popular choice for applications where space, air sealing, and moisture resistance are important considerations.
The best choice depends on your project location, climate, available space, moisture conditions, desired insulation performance, and budget.
If your project requires higher insulation performance in a limited space, closed-cell spray foam may be the better option.
Frequently Asked Questions
Is closed-cell spray foam better than open-cell?
Not necessarily for every application. Closed-cell foam generally provides higher R-value per inch and greater moisture resistance, while open-cell foam can be useful for larger cavities where more thickness is available.
Does open-cell spray foam absorb water?
Open-cell foam is more permeable to moisture than closed-cell foam. It should therefore be used only in applications where its moisture characteristics are appropriate.
Which spray foam has the highest R-value?
Closed-cell spray foam generally provides a higher R-value per inch than open-cell spray foam.
Can spray foam be used in a crawl space?
Yes, spray foam can be used in crawl spaces when the product and application are appropriate. Closed-cell foam is often considered for these areas because of its density and lower moisture permeability.
Is spray foam good for air sealing?
Yes. Both open-cell and closed-cell spray foam can help reduce air leakage when properly applied to suitable surfaces.
Can I use closed-cell spray foam for a DIY project?
Some closed-cell spray foam products are designed for DIY use. Always follow the product's application instructions, safety requirements, and recommended uses.
