Open Cell vs Closed Cell Spray Foam: Which One Should You Use in 2026?

Choosing between open-cell and closed-cell spray foam insulation is one of the most important decisions for your project’s efficiency, comfort, and long-term durability. The “right” choice depends on your climate, cavity depth, budget, and (most importantly) moisture exposure.

In this guide, you’ll get a clear side-by-side comparison of open cell vs closed cell foam, including R-values, costs, best use cases, and practical selection rules.

Quick Answer: Which One Should You Choose?

Here’s the simple rule if you’re deciding fast:

Choose CLOSED-CELL spray foam if you need higher R-value per inch, better moisture resistance, a built-in vapor retarder (in many assemblies), or extra rigidity; common for basements, crawl spaces, rim joists, exterior walls, and cold climates.
Choose OPEN-CELL spray foam if you want a more budget-friendly option for large areas, stronger sound absorption for interior walls, and you’re working in a dry environment where thickness is not a limitation.

Bottom line: Open-cell is often the better value for interior sound control and large dry attics. Closed-cell is typically the safer choice for moisture-prone areas, limited-depth cavities, and demanding climates.

Open Cell vs Closed Cell Spray Foam: A Quick Comparison

The following table summarizes the key differences at a glance.

Feature	Open-Cell Spray Foam	Closed-Cell Spray Foam	Why It Matters
R-Value per inch	~R-3.6	~R-5.6 to R-8 (varies by formulation)	Closed-cell insulates more in less space
Typical density	~0.5 lb/ft³	~2.0–3.0 lb/ft³	Closed-cell is more rigid and can add strength
Moisture behavior	Vapor-permeable (“breathable”)	Much less permeable; can function as a vapor retarder in many assemblies	Drives mold/condensation risk
Expansion	Higher expansion (fills cavities quickly)	Lower expansion; often applied in lifts	Affects application technique
Sound performance	Better absorption (mid/high frequencies)	Better blocking via rigidity + air seal	Choose based on noise goal
Typical installed cost	~$0.50–$1.50/sq ft	~$1.50–$4.50/sq ft	Closed-cell usually costs 2–3× more

Note: Exact R-values, permeability, and code requirements vary by product and local building code. Always confirm the specs of the foam you’re using.

Open-cell Spray Foam vs Closed-cell Spray Foam

What Is Open-Cell Spray Foam Insulation?

Open-cell spray foam is a low-density spray polyurethane foam with a “partially open” cell structure. Because the cells aren’t fully sealed, the foam is softer, more flexible, and more vapor-permeable than closed-cell.

Key characteristics of open-cell spray foam:

R-value: approximately R-3.6 per inch
Density: around 0.5 lb/ft³
Sound: excellent sound absorption for interior partitions
Expansion: expands aggressively to fill gaps and irregular cavities

Best use cases: Interior walls, ceilings, and attics in dry conditions where you have enough depth to reach your target R-value.

Primary limitation: Because open-cell foam is vapor-permeable, it is generally not the best choice for damp/below-grade environments. It may require a vapor-control strategy depending on your climate and assembly.

What Is Closed-Cell Spray Foam Insulation?

Closed-cell spray foam is a medium- to high-density spray polyurethane foam with fully sealed, tightly packed cells. This structure makes it rigid, strong, and far less vapor-permeable than open-cell. Closed-cell spray foam also tends to deliver a higher R-value per inch.

Key characteristics of closed-cell spray foam:

R-value: commonly ~R-5.6 to R-8 per inch (varies by product density/formulation)
Density: typically ~2.0–3.0 lb/ft³
Moisture: much better moisture resistance; can act as a vapor retarder in many assemblies (often around ~2 inches, depending on product)
Structure: rigid foam that can improve assembly stiffness (exact impact varies by wall/roof design)

Best use cases: Basements, crawl spaces, rim joists, exterior walls, unvented roof decks (where appropriate), and projects where cavity depth is limited but high performance is needed.

Medium-Density Closed-Cell Spray Foam (≈2 lb/ft³)

Medium-density closed-cell foam (around 2 lb/ft³) is the most common option in residential applications. It typically provides about R-5.6 to R-6.0 per inch and is widely used for exterior walls, rim joists, and crawl spaces, especially where moisture control and higher R-value per inch matter.

High-Density Closed-Cell Spray Foam (≈3 lb/ft³)

High-density closed-cell foam (around 3 lb/ft³) is used more often in demanding applications (for example, certain commercial/roofing or specialty assemblies) where maximum rigidity and performance are priorities. It can reach higher R-values per inch (often cited in the R-7 to R-8 range, depending on formulation) and delivers a tougher, more rigid finish; typically at a higher cost.

Types of Spray Foam Insulation Open Cell vs Closed-Cell

R-Value Comparison: Open Cell vs Closed Cell Performance

R-value is the headline metric in most open cell vs closed cell spray foam comparisons because it directly affects how much insulation you get per inch.

Open Cell Spray Foam R-Value per Inch

Open-cell is typically ~R-3.6 per inch. That means:

In a 3.5-inch (2×4) cavity: roughly ~R-12.6
In a 5.5-inch (2×6) cavity: roughly ~R-19.8
In an attic where 8–10 inches is feasible: Open-cell can reach code-level targets in many moderate climates

Closed Cell Spray Foam R-Value per Inch

Closed-cell typically delivers a higher R-value per inch; often around ~R-5.6 to R-8.0 for common residential formulations, with higher ranges possible depending on the product. That means:

In a 3.5-inch (2×4) cavity: roughly ~R-19.6 to ~R-28+ (depending on product)
In a 5.5-inch (2×6) cavity: roughly ~R-30.8 to ~R-44+ (depending on product)

What this means: Closed-cell is usually the practical choice if you need a high R-value but you’re working with limited depth.

If you're unsure about the R-value you need for your climate and application, read our blog post titled “Spray Foam Insulation R-Value: What It Means and How to Choose the Right Level” to confidently select the correct level.

Moisture Resistance and Vapor Control: The Make-or-Break Factor

Moisture risk is where many insulation projects go wrong, especially in basements, crawl spaces, rim joists, and exterior assemblies in humid or cold climates.

Why Closed-Cell Is Typically Used for Moisture-Prone Areas

Closed-cell’s sealed structure makes it far less vapor-permeable, so it’s commonly chosen for:

Basements and crawl spaces
Rim joists and below-grade transitions
Exterior walls where the condensation risk is higher
Areas with high humidity or potential water exposure

In many assemblies, closed-cell foam at sufficient thickness can function as a vapor retarder, reducing condensation risk inside cavities. The exact requirement depends on the foam’s tested permeability and your local code.

Open-Cell Foam: Where “Breathable” Helps and Where It Hurts

Open-cell foam is vapor-permeable. That can be beneficial in some interior assemblies because it allows drying potential. However, in moisture-prone areas or where condensation is likely, that permeability can be a liability unless the full wall/roof design includes proper vapor control.

General guidance:

Open-cell is commonly used in interior walls/ceilings and some attic assemblies (where appropriate).
Open-cell is generally not recommended for basements/crawl spaces or other persistently damp environments.

When installed correctly, spray foam insulation helps control moisture by sealing air leaks, and in many applications, spray foam insulation is waterproof, especially with closed-cell foam in areas with potential water exposure.

Soundproofing: Open Cell vs Closed Cell

Open-cell usually has the advantage if sound control is a major goal.

Why Open-Cell Spray Foam Is Better for Sound Absorption

Open-cell’s softer structure absorbs mid-to-high frequency sounds (voices, TV, general household noise) more effectively than rigid foams. This makes it a popular choice for:

Interior bedroom walls
Media rooms
Shared walls in multi-family buildings (as part of a full sound-rated assembly)

How Closed-Cell Handles Sound

Closed-cell can reduce noise mainly through air sealing and rigidity. It can help limit air leakage (which carries sound), but it generally doesn’t absorb sound as well as open-cell. For interior soundproofing goals, open-cell is usually preferred.

Cost Comparison: Open Cell vs Closed Cell Spray Foam

Cost varies by region, installer, thickness, and project complexity, but the typical relationship is consistent: closed-cell costs more.

Open Cell Spray Foam Cost per Square Foot

Open-cell is commonly cited at around $0.50 to $1.50 per sq ft (installed pricing varies widely by market and thickness). It’s often chosen for large-area projects where depth is available and budget is a priority.

Closed Cell Spray Foam Cost per Square Foot

Closed-cell is commonly cited at around $1.50 to $4.50 per sq ft (again, varying by region and thickness). It’s more expensive upfront, but it may reduce the need for additional vapor-control layers in some assemblies and can be the safer choice in moisture risk areas.

Which Is More Cost-Effective Long Term?

Open-cell: lower upfront cost; great value in the right dry applications
Closed-cell: higher upfront cost; often the better investment where moisture control, limited cavity depth, or maximum performance is required

For a deeper breakdown of real-world pricing and what drives your final quote, see our “2026 Spray Foam Insulation Cost per Sq Ft: A Complete Pricing Guide”.

Installation Differences: Expansion, Passes, and Curing

Both open-cell and closed-cell spray foam can deliver excellent results, but they behave differently during application.

Open-Cell Spray Foam Installation Basics

Open-cell expands rapidly and fills cavities quickly. Because of the aggressive expansion, it’s often efficient for large cavities. Curing time can be longer than for closed-cell, depending on the product and conditions.

Closed-Cell Spray Foam Installation Basics

Closed-cell expands less and is typically applied in thinner lifts (passes) to build thickness. It cures fast and becomes rigid quickly, which can be beneficial for certain assemblies, but it requires careful application to avoid issues with uneven build-up or improper lift thickness.

Safety note: Regardless of foam type, proper PPE and ventilation are essential during application, and cure time should be respected before re-occupying the space.

Best Uses: Where to Apply Open-Cell vs Closed-Cell Foam

Use-case clarity is what makes this “open cell vs closed cell spray foam” decision easy.

Where Open-Cell Spray Foam Works Best

Interior walls and ceilings (especially when sound is a priority)
Large attic areas in dry conditions where thickness is available
Projects where the budget is tight and the moisture risk is low

Where Closed-Cell Spray Foam Works Best

Basements and crawl spaces
Rim joists and below-grade transitions
Exterior walls in humid or cold climates (depending on assembly design)
Areas where cavity depth is limited but a high R-value is required

Conclusion: Choosing the Right Foam for Your Project

Choosing open-cell vs closed-cell spray foam comes down to matching the foam to your environment and goals:

Choose OPEN-CELL for budget-friendly coverage and sound absorption in dry, interior applications where thickness is available.
Choose CLOSED-CELL for higher R-value per inch, moisture resistance, and performance in basements, crawl spaces, rim joists, and limited-depth cavities.

When you align the foam type with moisture risk and cavity depth, you’ll get the best mix of comfort, durability, and long-term energy performance.

Need maximum R-value and moisture protection? Explore our Closed-Cell Spray Foam Insulation options to get the right coverage for your project.

FAQs: Open Cell vs Closed Cell Spray Foam

What is the difference between open and closed cell spray foam?

Open-cell foam is softer and more vapor-permeable with ~R-3.6 per inch. Closed-cell foam is rigid and less permeable with a higher R-value per inch (often ~R-5.6 to R-8 depending on product). Closed-cell is commonly used where moisture control and high performance in thin cavities are important.

Which is better: open-cell or closed-cell foam insulation?

Neither is universally “better.” Closed-cell is typically better for moisture-prone areas and limited-depth cavities. Open-cell is often better for interior sound absorption and budget-friendly coverage where moisture risk is low.

What is the R-value of open cell spray foam?

Open-cell spray foam is typically about R-3.6 per inch of thickness.

What is the R-value of closed-cell spray foam per inch?

Closed-cell spray foam commonly ranges from R-5.6 to R-8 per inch, depending on density and formulation. Check the product data sheet for the exact R-value.

Does closed-cell spray foam need a vapor barrier?

Often, no, closed-cell at sufficient thickness can function as a vapor retarder in many assemblies. However, requirements vary by climate zone, wall/roof design, and local code.

Can you use open-cell spray foam in a basement?

In most cases, open-cell is not recommended for basements because basements are inherently moisture-prone. Closed-cell is more commonly used for below-grade insulation due to better moisture resistance.

What are the benefits of spray foam insulation?

Spray foam insulation can improve air sealing, reduce drafts, and help lower heating and cooling costs over time. The benefits of spray foam insulation also include better moisture control by limiting humid air movement into cavities, long-term durability, and potential noise reduction (especially with open-cell in interior walls).

Open Cell vs Closed Cell Spray Foam: Complete Comparison Guide (2026)