Understanding the Two Types of Spray Foam

Spray foam insulation is one of the most effective solutions for sealing and insulating buildings today. As a leading spray foam manufacturer and supplier, PolyCon offers both open-cell spray foam and closed-cell spray foam, each engineered for specific performance needs on the job site. While both provide excellent air sealing, they perform very differently when it comes to moisture control, structural support, and total project cost.

Open Cell Spray Foam

Open-cell spray foam is a soft, flexible, and highly expandable insulation material. When applied, it expands up to 100 times its original liquid volume, allowing it to flow deep into cavities and effectively seal gaps and hard-to-reach areas. This makes it a perfect option for interior applications where air sealing and sound absorption are primary goals. With a density of approximately 0.5 lb./ft³ and an R-value of R-3.5 to R-3.7 per inch, it provides reliable thermal performance in a lightweight form.

Contractors often turn to open-cell foam for its budget-friendliness and ease of installation in tight spaces, such as interior walls and ceilings. It is also the preferred option for sound-sensitive areas such as media rooms, home offices, and bedrooms, where its porous structure helps dampen noise transmission. For cost-conscious builds where cavity depth is not a limiting factor, open-cell spray foam offers a strong balance of performance and value. While it acts as an excellent air barrier, it is not a vapor barrier, so it is best suited for dry, interior applications.

• Density: ~0.5 lb/ft³

• R-Value: ~R-3.5 to R-3.7 per inch

• Expansion: Up to 100x its liquid volume

• Air Barrier: Yes

• Moisture Barrier: No

Where It Works Best:

• Interior walls and ceilings

• Sound-sensitive areas like media rooms and offices

• Budget-conscious builds where thickness isn’t an issue

Why Contractors Use It:

• More affordable than closed-cell

• Great at dampening sound

• Expands to fill irregular cavities

• Easy to work with in tight spaces

Closed-Cell Spray Foam

Closed-cell spray foam is a dense, rigid insulation that offers superior strength and moisture resistance. With a density of about 2 lb./ft³ and an R-value of R-6 to R-7 per inch, it delivers high thermal performance in a thinner profile. It expands approximately 30 times its liquid volume, creating a tight, impermeable seal that blocks both air and moisture. This makes closed-cell foam an effective vapor barrier, protecting structures from water intrusion and condensation in harsh conditions.

This type of foam is ideal for exterior walls, roofs, basements, and crawl spaces where moisture exposure and weather are concerns. Its rigidity also adds structural strength to wall and roof assemblies, making it a well-liked choice for metal buildings and commercial projects. Contractors rely on closed-cell foam in thin cavities that need maximum insulation value and in places requiring long-term durability. While the upfront cost is higher than that of open-cell, its thermal performance and moisture control often yield significant energy savings throughout the life of the building.

• Density: ~2 lb/ft³

• R-Value: ~R-6 to R-7 per inch

• Expansion: ~30x its liquid volume

• Air Barrier: Yes

• Moisture Barrier: Yes

Where It Works Best:

• Exterior walls, roofs, and basements

• Areas exposed to moisture or weather

• Thin cavities that need high insulation value

• Metal buildings and commercial projects

Why Contractors Use It:

• Delivers top-tier insulation in less space

• Provides moisture control in damp environments

• Increases structural rigidity

• Long-lasting and durable

Differences Between Open-Cell and Closed-Cell Foam

Comparing the Cost of Open-Cell vs. Closed-Cell Foam

Cost comparison both in wholesale and retail for different R values.

The cost difference between open-cell and closed-cell spray foam comes down to material density, performance, and application.

At the wholesale level, closed-cell foam is more expensive per board foot because of its higher density and chemical content. At retail, contractors typically see closed-cell projects priced 50% to 100% higher than open-cell for the same thickness.

However, because closed-cell achieves a higher R-value per inch (R-6 to R-7 vs. R-3.5 to R-3.7 for open-cell), you can use less material to reach the same insulation target, which can offset some of the upfront cost in high-performance builds. For projects where budget is the primary driver and cavity depth allows for thicker insulation, open-cell remains the more economical choice.

Choosing the Best Insulation for Your Specific Needs

Choosing the right spray foam for insulation comes down to your project goals. If you are insulating a crawlspace, basement, or any exterior-facing surface, closed-cell is likely your best bet. For interior partitions where sound control and budget are the priorities, open-cell is the right call.

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