Open Cell vs Closed Cell Spray Foam

Last updated: 5 November 2026

Two Types of Spray Foam

Almost all spray foam insulation in UK lofts is one of two types: open cell or closed cell. Both start as two liquids mixed at the spray gun, which expand and set within seconds. The difference is what happens to the tiny bubbles — the cells — inside the foam as it sets.

• Open cell foam: the cells burst open, leaving a soft, light, spongy material.
• Closed cell foam: the cells stay sealed, making the foam dense, rigid and hard.

How to Tell Which You Have

From the loft hatch, without disturbing the foam more than necessary:

• Press lightly with a gloved finger. Open cell foam gives and springs back; closed cell foam barely moves.
• Look at the surface. Open cell foam is often paler, softer-looking and more uneven; closed cell foam tends to look harder and smoother, sometimes slightly yellowed.
• Check the paperwork. An installer’s invoice or guarantee may name the product or type.

If you’re unsure, clear photos from the hatch are usually enough for us to tell.

Open Cell vs Closed Cell at a Glance

Why the Type Matters for Lenders and Surveyors

Both types hide the roof structure, which is why surveyors flag them. Closed cell foam draws extra attention because it can stop a roof drying out, and in older Bristol roofs — some with original slates and no felt — trapped moisture is a real concern. Lender policies don’t always distinguish between the two, so check what yours requires.

What It Means for Removal Cost

Removal is mostly labour, so the foam type has a big effect on price. Open cell foam on part of a small terrace loft in Southville or Easton will usually sit near the lower end of the guide ranges. Rigid closed cell foam across a large hipped roof in Henleaze or Brislington will usually sit higher. More on our closed cell spray foam removal page.