Open-Cell vs Closed-Cell Spray Foam: What’s the Difference?

If you’ve found spray foam insulation in your loft — or had a survey flag it — you might be told it’s “open-cell” or “closed-cell.” But what does that actually mean? And why does it matter?

The difference between these two types of spray foam affects:

• How breathable your loft is
• Whether your home is mortgageable
• How risky it is for moisture, rot, or structural issues

Let’s break it down clearly, without the sales fluff.

What Is Open-Cell Spray Foam?

Open-cell foam is:

• Soft and spongy to the touch
• Less dense, allowing air and some moisture vapour to pass through
• Typically cheaper and easier to install
• Often used in interior walls and ceilings (not always roofs)

It’s sometimes marketed as “breathable foam,” but that doesn’t mean it’s risk-free. If installed too thickly or without proper ventilation, it can still trap moisture — especially in unventilated lofts.

That said, open-cell foam is less likely to cause survey problems compared to closed-cell — but only if installed correctly and documented.

What Is Closed-Cell Spray Foam?

Closed-cell foam is:

• Rigid and hard when cured
• Dense, with tightly packed air cells
• Highly effective as an air barrier
• Commonly used in lofts and roofing applications

This is the type that most often causes issues in UK homes. Why?

• It blocks airflow completely
• It seals directly over rafters, nails, and membranes
• It hides timber from inspection
• It traps condensation behind the foam

Most mortgage lenders reject properties with closed-cell spray foam — especially in older homes with timber roofs.

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Can Either Type Be Removed?

Yes. At Snug & Secure, we safely remove both open-cell and closed-cell spray foam from UK homes.

We’ll identify what’s in your loft, remove it without damaging the structure, and reinsulate with breathable, regulation-compliant materials.

Final Thoughts

Whether it’s open-cell or closed-cell, spray foam can cause problems if not installed perfectly — and in most older homes, it rarely is.

If you’re not sure what’s in your loft, get in touch for a free assessment — or browse our full blog to learn more about protecting your home’s value, safety, and warmth.