How Does Spray Foam Insulation Work?

At Complete Insulation, we specialize in helping builders and homeowners across Middle Tennessee make smart choices about their insulation. One question we often get is, “How does spray foam insulation work?” Let’s break it down.

Spray foam insulation is a high-performance material that expands on contact to fill gaps, seal air leaks, and create an effective thermal barrier. It’s widely used in homes and commercial buildings throughout Nashville for its energy-saving benefits and durability—especially in attics, crawl spaces, and wall cavities.

But how does it really work? 

What Is Spray Foam Insulation?

Spray foam insulation is a liquid mixture that expands into a thick foam when sprayed. It’s applied directly to surfaces like roof decks, exterior walls, garage ceilings, crawlspaces and more. Once it expands and cures, it forms an airtight seal that helps regulate indoor temperatures and improve energy efficiency.

There are two main types of spray foam:

• Open-cell spray foam – Lightweight and flexible, open-cell foam is great for sound dampening and indoor applications. It’s more affordable, but has a lower R-value per inch compared to closed-cell foam.
• Closed-cell spray foam – Denser and more rigid, closed-cell foam provides a higher R-value, acts as a vapor barrier, and adds structural support.

Both types work well, but the choice depends on your specific insulation goals along with your budget.

How Spray Foam Insulation Works

Spray foam is made of two chemical components—usually a polyol resin and isocyanate—that are combined at the tip of a spray gun during installation. As soon as the materials mix, they begin to expand rapidly—sometimes up to 120 (open cell) times their original volume. This allows the foam to fill even the smallest cracks and crevices. Once cured, the foam forms a continuous insulation layer that prevents:

• Heat transfer (keeps warm air in during winter and out during summer)
• Air leakage (reduces drafts and improves indoor air quality)
• Moisture intrusion (especially with closed-cell foam)

This makes spray foam attic insulation particularly valuable in hot and humid climates like we have here in Middle Tennessee.

Should I Spray Foam My Attic Roof?

If you’ve been wondering “Can I spray foam my attic?” or “Should I spray foam my attic roof?”—you’re not alone. The attic is one of the most common and most effective places to install spray foam.

Spraying foam on the attic ceiling (roof deck) helps create a “conditioned attic” by sealing out hot air and moisture, rather than relying on vents and loose-fill insulation in the attic floor. This is especially helpful in homes with HVAC systems or ductwork in the attic, as it improves system efficiency and reduces energy waste.

Installation Considerations

Upfront Cost

For some the upfront cost can be an issue. It typically costs more than fiberglass or cellulose insulation upfront, though the overall performance and energy savings often offset that over time.

Installation Quality Matters

Poor application can lead to spray foam insulation issues, such as gaps, improper expansion, or off-gassing. Always choose an experienced and approved installer (like us!) to avoid these foam insulation problems.

Moisture Trapping in Open-Cell Foam

In humid environments – such as a crawl space, open cell spray foam insulation can absorb moisture. That’s why we only install closed cell spray foam insulation in a crawl space.

Limited DIY Options

Spray foam requires specialized equipment, personal protection equipment (PPE) and knowledge. Improper installation can lead to costly mistakes that can damage the substrate it is applied to.

Compatibility with Roofing Systems

There are some spray foam insulation roof problems when it’s not installed properly or if the roofing material doesn’t allow for adequate moisture management. This is why we assess each attic carefully before recommending attic foam insulation.

The Bottom Line: Is Spray Foam Right for You?

Spray foam is one of the best insulation options available today. It offers powerful energy savings, superior air sealing, and long-term durability. 

If you’re asking, “Should I spray foam my attic?” or “What are the negatives of spray foam?”—let us help you make the right decision for your home or project. We’re not just spray foam installers—we’re insulation problem solvers.

Get Expert Spray Foam Installation in Nashville & Middle Tennessee

Whether you’re dealing with a hot attic, drafty walls, or moisture-prone crawl space, Complete Insulation is your trusted partner for professional spray foam insulation. Our experienced team will guide you through the entire process—from material selection to clean, precise installation.

Contact Complete Insulation today to schedule your free estimate and learn if spray foam insulation is right for your home or building. Let’s make your property more efficient, comfortable, and protected from the elements.