Open-Cell vs. Closed-Cell Spray Foam: A Cost and Performance Breakdown

Choosing the right insulation often comes down to open-cell versus closed-cell spray foam. The fundamental difference lies in their cellular structure and density. Closed-cell foam is dense, rigid, and acts as an air, vapor, and water barrier. Its compact structure gives it a high R-value per inch, making it a powerful insulator. In contrast, open-cell foam is lighter, more flexible, and sponge-like. It’s an excellent air barrier and provides superior sound dampening, but it is vapor-permeable and offers a lower R-value per inch.

Deciding between them isn’t about which one is better overall, but which is the right fit for a specific application, budget, and performance goal. This guide breaks down the key performance metrics and cost considerations to help you make an informed choice. Drawing from extensive field experience, Wegner Insulation provides a practical look at where each type of foam excels and why.

Understanding the Structural Differences

The names “open-cell” and “closed-cell” refer to the tiny bubbles, or cells, that form when the foam’s two chemical components mix and expand.

• In open-cell spray foam, the cells are intentionally left open, creating a structure similar to a rigid sponge. This structure makes the foam soft, flexible, and light, with a typical density of around 0.5 pounds per cubic foot. Its pliability allows it to expand and contract with a building’s movement, which helps maintain an airtight seal over time.
• Closed-cell spray foam, on the other hand, is made of cells that are completely sealed and packed tightly together. These cells are filled with a special gas, known as a blowing agent, which is what gives the foam its high insulating power. With a density of around 2.0 pounds per cubic foot, closed-cell foam is significantly more rigid and durable. These structural characteristics directly influence how each foam performs in key areas.

Performance Metrics Head-to-Head

While both foams insulate, their performance varies greatly across several key areas. Understanding these differences is essential for selecting the right material for your project.

R-Value and Thermal Resistance

R-value measures an insulation’s ability to resist heat flow. The higher the R-value, the better the insulation.

• Closed-Cell: This type offers a high R-value, typically ranging from R-6 to R-7 per inch. This makes it ideal for applications where you need maximum insulation in a limited space, such as 2×4 wall cavities.
• Open-Cell: This foam provides an R-value of about R-3.5 to R-4 per inch. While lower than closed-cell, it still delivers excellent thermal performance, especially in deeper cavities like attics, where thickness isn’t a constraint.

Air and Vapor Permeability

Both foam types are effective air barriers, stopping drafts and air leakage that can account for significant energy loss. Their handling of moisture, however, is a major point of difference.

• Closed-Cell: It acts as a vapor barrier, meaning it blocks the movement of moisture. At a depth of about 1.5 to 2 inches, it has a very low perm rating (typically less than 1.0), which helps prevent moisture from entering a wall assembly. This makes it suitable for below-grade applications like basements and crawl spaces.
• Open-Cell: This foam is vapor-permeable, allowing moisture to pass through it. This can be an advantage in certain climates and wall assemblies, as it lets the structure breathe and dry out if it gets wet.

Structural Strength

The density of closed-cell foam gives it a unique advantage.

• Closed-Cell: It adds significant racking strength and rigidity to walls and roofs. A study mentioned by Accufoam shows that walls insulated with closed-cell foam can be up to 300% stronger. This can be particularly useful in areas prone to high winds or heavy snow.
• Open-Cell: Its soft, flexible nature means it does not add structural support to a building.

Sound Dampening

For controlling noise, the less dense structure of open-cell foam is a clear winner.

• Open-Cell: It excels at absorbing sound waves, making it roughly twice as effective as closed-cell foam for noise reduction. Its porous structure traps sound, making it a great choice for media rooms, offices, and interior walls between bedrooms and bathrooms.
• Closed-Cell: It provides some sound dampening due to its air-sealing properties, but its rigid structure reflects sound more than it absorbs it.

A Practical Cost Comparison

Cost is often a deciding factor. Closed-cell foam is more expensive per board foot (a 12x12x1-inch square) than open-cell foam. This is because it uses more chemical material to achieve its high density. While professional installation costs vary, you can generally expect closed-cell foam to be priced higher.

However, the “cheaper” option isn’t always the most cost-effective. Since closed-cell has a higher R-value per inch, you need less of it to achieve a specific insulation target. This can sometimes narrow the final price gap, especially in shallow cavities.

Feature Snapshot: Open-Cell vs. Closed-Cell

Feature	Open-Cell Spray Foam	Closed-Cell Spray Foam
R-Value per Inch	R-3.5 to R-4.0	R-6.0 to R-7.0
Vapor Barrier	No (Vapor Permeable)	Yes (at 1.5-2″ depth)
Air Barrier	Yes	Yes
Structural Strength	No	Yes, adds rigidity
Sound Absorption	Excellent	Fair
Cost	Lower per board foot	Higher per board foot

Where to Use Each Type of Foam

Applying the right foam in the right place is key to maximizing its benefits.

Ideal Applications for Open-Cell Foam

• Interior Walls: Its superior sound-dampening properties make it perfect for reducing noise transfer between rooms.
• Attic Rooflines: In an unvented attic assembly, open-cell foam provides excellent air sealing and thermal insulation, allowing any potential moisture to dry through the material.
• Floors Between Stories: Helps reduce airborne sound transmission from one level of a home to another.

Bonus Tip: When using open-cell foam on a roof deck, it’s a good practice to paint the sheathing with a vapor-retarding primer first, especially in humid climates, to manage moisture diffusion.

Best Uses for Closed-Cell Foam

• Exterior Walls: Provides a high R-value in limited space and acts as a vapor barrier to protect the wall assembly.
• Basements & Crawl Spaces: Its resistance to moisture makes it the best choice for below-grade applications where dampness is a concern.
• Metal Buildings: Adheres well to steel and adds structural rigidity while preventing condensation.
• Areas Prone to Flooding: The Federal Emergency Management Agency (FEMA) often recommends closed-cell foam in flood-prone regions because it rejects bulk water, according to Spray Foam Insulation NYC.

Things to Consider Before Making a Decision

Before you choose, think about these factors:

• Your Climate: In very cold climates, the higher R-value and vapor barrier of closed-cell foam might be necessary. In more moderate or mixed climates, open-cell could be sufficient.
• Building Codes: Local building codes may have specific requirements for R-values and vapor retarders. Always check what’s needed for your area.
• Project Budget: The material cost for closed-cell is higher. Weigh the upfront investment against long-term energy savings and performance benefits.
• Long-Term Goals: Are you prioritizing maximum energy efficiency, soundproofing, or structural reinforcement? Your primary goal will steer your decision.

Bonus Tip: Regardless of which foam you use, the U.S. Department of Energy stresses the importance of ensuring the product is installed correctly by a trained professional and separated from living spaces with a proper thermal barrier like drywall.

Making the Right Choice for Your Project

The debate between open-cell and closed-cell spray foam isn’t about finding a single winner. It’s about selecting the right tool for the job. Closed-cell foam provides an all-in-one solution for thermal, air, and moisture control with the added benefit of structural reinforcement. Open-cell foam offers a cost-effective way to achieve a superb air seal and excellent sound control.

Ultimately, the best choice depends on your specific project. Evaluate your home’s needs, your local climate, your budget, and your performance priorities. A thorough assessment of these factors will lead you to the insulation that delivers the most value and comfort for years to come.

Get a Professional Assessment

Navigating the technical differences between foam types can be complex. A professional evaluation is the best way to determine the ideal solution for your property. For a detailed consultation tailored to your project’s specific needs, contact Wegner Insulation. The team can provide an expert recommendation based on years of hands-on experience. Reach out by phone at (406) 607-8476 or send an email to [email protected] to discuss your insulation requirements and get a clear path forward.

Frequently Asked Questions

Can you mix open-cell and closed-cell foam in the same house?

Absolutely. It’s common practice to use a “hybrid” approach, applying closed-cell foam in areas like basements and rim joists while using open-cell foam in walls and attics to balance cost and performance.

Is spray foam flammable?

Spray foam is a plastic material and is combustible. However, it’s treated with fire retardants, and building codes require it to be covered by an approved thermal barrier, such as 1/2-inch drywall, to separate it from the interior living space.

How long does spray foam last?

When installed correctly, spray foam insulation should last for the life of the building. Unlike some other insulation types, it doesn’t sag, settle, or decompose over time, maintaining its performance for decades.

Sources

• Accufoam – This guide explains the structural reinforcement properties of closed-cell spray foam, including data on its strength.
• U.S. Department of Energy – This page provides official guidance on the safe and effective installation of spray foam, including the need for a thermal barrier.