If you’ve been researching spray foam insulation, you’ve probably heard people say closed cell spray foam is the best.
But the better question is… best for what?
Closed cell spray foam is a powerful insulation material, but it’s not the right fit for every project. Good insulation decisions aren’t about hype – they’re about using the right building science for your space.
Let’s break it all down so you can understand what closed cell spray foam insulation is, how it works, where it shines, and where it doesn’t.
Key Points: Closed Cell Spray Foam at a Glance
• Closed cell spray foam is a low-expanding, rigid insulation that creates an air seal.
• It has a high R-Value of about R-6 to R-7 per inch.
• Commonly used in pole barns, vans, tiny homes, and commercial buildings.
• It acts as an air barrier and moisture barrier.
• Closed cell spray foam rejects bulk water and does not absorb moisture.
• It is durable, mold-resistant, and ideal for tight spaces.
• Not every home or project requires closed cell – application matters.
What is Closed Cell Spray Foam?
Closed cell spray foam is a low-expanding, rigid spray foam insulation that creates an air seal wherever it’s installed.
Unlike fluffy or fibrous insulation materials, closed cell foam hardens after application. That rigid structure is what gives it its strength, durability, and high insulating performance.
One of the biggest reasons homeowners and builders are drawn to it is its impressive R-Value.
What is the R-Value of Closed Cell Spray Foam?
The R-Value of closed cell spray foam is one of its biggest selling points.
- Closed cell spray foam R-Value R-6 to R-7 per inch.
This high R-Value makes it especially useful in projects where space is limited, but insulation performance still matters, like van walls, tiny homes, or commercial retrofits.
Where Closed Cell Spray Foam Insulation is Commonly Used
Closed cell spray foam insulation really shines in environments that demand strength, moisture control, and efficiency.
You’ll commonly see it used in:
- Pole barns
- Vans and camper vans
- Tiny homes
- Commercial buildings
While open cell spray foam is usually recommended for residential homes, there are situations where closed cell is the better fit, especially when moisture resistance or added rigidity is required.
How Does Closed Cell Spray Foam Work?
Closed cell spray foam is sprayed directly into wall cavities, ceilings, or other building assemblies.
Because it has a low expansion rate, it expands just enough to:
- Seal gaps and cracks
- Stop air leaks
- Create a continuous insulation layer
Once cured, it forms a strong air barrier and moisture barrier, helping reduce drafts, condensation, and moisture-related issues.
Moisture Resistance and Flood Classification
Here’s an important, but often misunderstood, fact:
FEMA classifies closed cell spray foam as highly resistant to floodwater.
This doesn’t mean it’s waterproof in every situation or that you should buy it just for that reason. What it does mean:
- Closed cell spray foam rejects bulk water
- It does not absorb moisture
The result is more consistent indoor temperatures and fewer condensation and moisture problems over time.
Benefits of Closed Cell Spray Foam Insulation
Closed cell spray foam has some clear advantages when it’s used in the right application.
Durability and Strength
Closed cell foam is rigid and tough.
In areas like pole barns or vans, it can often be left exposed and still hold up to everyday wear and tear.
Mold Resistance
Mold and mildew need moisture to grow.
Since closed cell spray foam doesn’t absorb water, it doesn’t provide the conditions that mold needs to thrive.
Low Expansion Rate
That controlled expansion makes closed cell spray foam ideal for tight or shallow cavities, like:
- Van walls
- Tiny home framing
- Metal structures
High Performance in Demanding Environments
The bottom line: closed cell spray foam is built for environments that need strength, moisture control, and efficiency.
What is Closed Cell Spray foam Made Of?
Closed cell spray foam insulation is created on-site using two liquid components:
- “A” side: Isocyanates
- “B” side: Resins, blowing agents, flame retardants, and catalysts
When the “A” side and “B” side combine, a chemical reaction occurs. The foam is formed and sprayed into place, where it expands slightly and seals the cavity.
Safety Notes Homeowners Should Know
Any time spray foam insulation is involved, it’s smart to ask the right questions.
Before installation, ask your insulation contractor:
- Does the closed cell spray foam have low VOCs?
- Is it Class One Fire-Rated?
- What is the reoccupancy time after installation?
An experienced contractor should be able to answer these clearly and confidently.
What Does the Closed Cell Spray Foam Installation Process Look Like?
The installation process is straightforward, but there is prep involved.
Before Installation
- Existing insulation must be removed
- Floors, windows, doors, and surfaces are protected with plastic
During Installation
- The crew runs a hose into the work area
- Closed cell spray foam is applied to the cavities
- The foam cures in place
After Installation
A good contractor will:
- Walk through the project with you
- Make sure the foam is installed properly
- Clean up the job site before leaving
Is Closed Cell Spray Foam Always the Best Choice?
Not necessarily.
Closed cell spray foam is excellent at what it’s designed to do, but that doesn’t mean it’s the best insulation for every home or every project.
The right choice depends on:
- The structure
- The environment
- Moisture concerns
- Available space
- Overall building science goals
Building Science Over Buzzwords
Closed cell spray foam insulation is durable, moisture-resistant, and high-performing when it’s used in the right place.
The key isn’t choosing insulation based on what’s “best.” It’s choosing what’s best for your specific space.
If you want to learn more about foam insulation, building science, and making smarter comfort decisions for your home, check out our Learning Center for more articles, videos, and resources.
Related Articles
Problems with Closed Cell Spray Foam Insulation
Why Closed Cell Spray Foam Insulation is a Popular Choice for Homeowners
What is Open Cell Spray Foam Insulation?
Frequently Asked Questions About Closed Cell Spray Foam
What is closed cell spray foam insulation best used for?
Closed cell spray foam insulation is best used in environments that need high R-Value, moisture resistance, and durability, such as pole barns, vans, tiny homes, and commercial buildings.
What is the R-Value of closed cell spray foam?
The R-Value of closed cell spray foam is typically R-6 to R-7 per inch, making it one of the highest-performing insulation materials available.
Is closed cell spray foam waterproof?
Closed cell spray foam is water impermeable, which means it doesn’t allow water or moisture to move through it; it also rejects bulk water and does not absorb moisture.
Can closed cell spray foam be left exposed?
In some applications – such as pole barns and vans – closed cell spray foam can be left exposed, depending on local building codes and use of the space.
