Closed Cell vs. Open Cell Spray Foam: What You Need to Know Before Insulating Your Attic

If you’re reading this post, you’re probably trying to figure out what kind of insulation you’ll want to use in your attic or home. Well, you’re in the right place because at Leak Stoppers Inc. we frequently advise customers on what to do with attic spaces and insulation. That’s because the space beneath a roof plays a critical role in how long that roof will last, and, if the warranty will stay valid or end up void.

When it comes to insulating these spaces, spray foam insulation is one of the most effective and energy-efficient options available. But not all spray foam is created equal. There are two main types—Open Cell and Closed Cell—and choosing the wrong one for your attic or roof deck could lead to some very costly damage down the road. Let’s break down the differences and explore why we at Leak Stoppers Inc. always recommend Closed Cell Spray Foam as the smarter choice for attic insulation.

What Is Spray Foam Insulation?

Spray foam insulation is a chemical product created by mixing isocyanate and polyol resin. When sprayed, it expands and hardens into a solid foam that seals gaps and provides thermal insulation. It comes in two varieties:

Open Cell Spray Foam

• Structure: Made up of tiny cells that are not completely closed.
• Texture: Soft and spongy.
• R-Value: Lower (typically around R-3.5 to R-4 per inch).
• Air Barrier: Yes.
• Moisture Barrier: No.
• Best For: Interior walls and soundproofing.

Closed Cell Spray Foam

• Structure: Composed of completely closed cells.
• Texture: Rigid and dense.
• R-Value: Higher (around R-6 to R-7 per inch).
• Air Barrier: Yes.
• Moisture Barrier: Yes.
• Best For: Attics, basements, crawl spaces, and exterior walls.

Why Open Cell Spray Foam Is a Risk for Attics

While Open Cell foam is great for soundproofing and interior applications, it’s a poor choice for insulating attics or roof decks. Here’s why:

• Moisture Permeability: Open Cell foam allows water vapor to pass through. In an attic, this means moisture from inside the home can reach the underside of the roof.
• Rot Risk: Over time, trapped moisture can lead to wood rot, mold growth, and structural damage to the roof deck.
• No Moisture Protection: It doesn’t provide a vapor barrier, leaving your roof vulnerable to long-term deterioration.

Why Closed Cell Spray Foam Is Ideal for Attics

Closed Cell Spray Foam is the gold standard for attic insulation. Here’s what makes it superior:

• Moisture Blocking: It acts as a vapor barrier, preventing water vapor from reaching the roof deck.
• Air Sealing: It creates an airtight seal, reducing energy loss and improving HVAC efficiency.
• Structural Support: Its rigid nature adds strength to roof decking and framing.
• Rot Prevention: By keeping moisture out, it protects the roof from rotting from underneath.

Warranty Check: Don’t Forget the Attic Baffles!

When using Closed Cell Spray Foam in an attic, maintaining ventilation is crucial. That’s because ventilation not only has an immediate effect on the climate in your home, but it also plays a part in the validity of your roof’s warranty. That’s where attic baffles come in:

• What Are Baffles?: Baffles are channels that maintain airflow from soffit vents to the attic space.
• Why They Matter: Without proper ventilation, even the best insulation can trap moisture. Baffles ensure that air continues to circulate, preventing condensation buildup.
• Installation Tip: Always install baffles before applying spray foam to ensure they remain unobstructed.

Final Thoughts

Choosing the right spray foam insulation is about more than just energy savings—it’s about protecting your home’s structural integrity while providing year-round comfort. For attic applications, Closed Cell Spray Foam is our clear winner. It blocks moisture, seals air leaks, and helps prevent costly roof rot. Just remember to pair it with proper ventilation using attic baffles, and you’ll enjoy a well-insulated, long-lasting roof system.

Need help with insulating your home or attic? Call Leak Stoppers Inc. today at 631-669-1570 or click here to use our online contact form and let our expert team help you ensure any investment in your home is one that will last a lifetime.