Closed Cell Insulation: Definition and What it is

What is Closed Cell Insulation?

Closed-cell spray foam is a high-performance insulation with tightly packed cells that don't allow air or moisture to penetrate. It offers the highest R-value per inch of any common insulation material (R-6 to R-7) and adds structural strength to walls and roofs.

Closed-cell foam consists of completely enclosed cells filled with gas that resist heat transfer. The rigid structure creates an impermeable air and moisture barrier while providing excellent R-value in minimal thickness—critical for space-constrained applications. The foam expands to about 1 inch during application and cures to a dense, rigid material. Unlike open-cell foam, closed-cell is moisture-resistant and can be used in below-grade applications, rim joists, and exterior walls without additional vapor barriers in most climates.

Closed-Cell Foam Applications

• Standard Density: 1.75-2.0 lbs/cu ft, most common for residential applications
• Medium Density: 2.0-3.0 lbs/cu ft, enhanced structural support and impact resistance
• High Density: 3.0+ lbs/cu ft, specialty applications requiring maximum strength
• Low-GWP Formulations: Using blowing agents with reduced global warming potential

When to Choose Closed-Cell Foam

Closed-cell spray foam excels in applications requiring maximum R-value in limited space, moisture resistance, or structural enhancement. Ideal for basement walls, rim joists, cathedral ceilings, metal buildings, and under concrete slabs. It's the preferred choice in flood-prone areas and for creating conditioned attic spaces. The higher cost is justified when space is limited, moisture is a concern, or when air sealing and insulation need to be accomplished in one application. Building codes may require thermal barriers (drywall) over spray foam for fire safety.

Benefits of Closed Cell Insulation

• Highest R-value per inch (R-6 to R-7) of common insulation materials
• Superior air sealing eliminates drafts and infiltration
• Moisture barrier properties prevent water vapor transmission
• Adds structural strength to walls and roofs (racking resistance)
• Long-lasting performance with minimal settling or degradation
• Effective in limited-space applications

Closed Cell Insulation Cost

Closed-cell foam is the most expensive insulation option but offers unmatched performance and multi-functional benefits.

• Installation cost typically $3-$7 per square foot (varies by thickness)
• Target R-value and required thickness
• Application area and accessibility
• Project size (larger projects get better per-square-foot rates)
• Regional contractor availability and competition
• Removal of existing insulation if required

Related Services and Resources

Related Terms

• Spray Foam Insulation: Definition and What it is
• Open Cell Insulation: Definition and What it is
• Polyurethane Foam Insulation: Definition and What it is
• R-Value Insulation: Definition and What it is

References

• Energy.gov - Foam Insulation Types
• ENERGY STAR - Seal and Insulate
• Wikipedia - Thermal Insulation
• Energy.gov - Insulation (Energy Saver)
• National Insulation Association - Insulation Basics
• ICAA - Insulation for Consumers