Open cell vs closed cell spray foam: how to tell which is in your loft
Open cell foam is soft, pale and gives way under a thumb; closed cell is hard, dense and does not move at all, and the two cost different amounts to remove. A free inspection confirms which one you have and prices the job in writing.
The four second test
Press a thumb into the foam. If it dents easily and feels spongy, it is almost certainly open cell. If your thumb makes no impression at all and it feels like pressing on rigid board, it is closed cell. Colour is a useful second check but never the only one, because product shades vary between manufacturers and darken slightly with age.
Why this is the first question, not the last
Every removal quote, every cost figure and every question about membrane damage depends on which foam is in your loft. Open cell and closed cell are made differently, behave differently once sprayed, and come off the timber in completely different ways. A firm that quotes without establishing which one you have is guessing, and the gap between the two removal rates is wide enough to matter.
If you still have the original installation paperwork, a BBA or KIWA certificate will name the exact product, which settles the question instantly. Most people asking this do not have that paperwork to hand, so the checks below are for everyone else.
From the loft hatch
Five things to check before you touch anything
Look before you climb in
Shine a torch across the slope. Note the colour, whether the surface looks even and spongy or smooth and hard, and where it has been sprayed: over the rafters with a visible gap at the eaves, or straight onto the underside of the tiles with no gap at all.
Do the thumb test
Press firmly with a thumb on an accessible patch. Open cell dents and often crumbles slightly at the edge of the dent. Closed cell does not move. This single test tells most people which they have.
Check the colour, but do not rely on it alone
Open cell is usually pale, cream or off white. Closed cell is usually darker, tan, brown or grey. Products vary between manufacturers and foam yellows slightly with age, so use colour to confirm the thumb test, not to replace it.
Look at a cut or damaged edge
Where the foam has been disturbed, cut, or has a broken corner, you can see the cell structure. Open cell looks like an open, spongy structure, similar to a bath sponge. Closed cell looks tight and glassy, with almost no visible air pockets.
Check for a ventilation gap at the eaves
Open cell is more often installed with a gap left at the eaves for air to move. Closed cell is more often sprayed flush with no gap. This is not a certain test on its own, but it is a useful clue and it matters for a separate reason: a missing ventilation gap is the configuration most likely to trap moisture.
Side by side
Open cell and closed cell compared
Eight things that differ between the two, in the order they usually matter to a homeowner.
| Feature | Open cell | Closed cell |
|---|---|---|
| Appearance | Pale cream to off white, an even spongy surface, sometimes visibly uneven or bubbled. | Usually darker, tan to brown or grey, with a smoother, harder, almost plasticky surface. |
| Feel under thumb pressure | Gives way easily. It dents, and often crumbles a little at the edge of the dent. | Does not move. Pressing on it feels like pressing on rigid board, with no give at all. |
| Density | Low density, light and soft. | High density, rigid and heavy for its size, closer to a solid material than a foam. |
| Colour | Usually pale: cream, off white or pale yellow, though the exact shade varies by product and age. | Usually darker: tan, brown, grey or occasionally black. Colour alone should never be the only test. |
| Where it is usually sprayed | Between and over the rafters, often with a visible gap left at the eaves for ventilation. | Direct onto the underside of the tiles or the sarking felt, frequently with no gap at all. |
| Vapour behaviour | More open to vapour movement, so moisture is more likely to find a way out where ventilation exists. | Effectively seals the roof. Moisture trapped behind it has nowhere to go. |
| Removal cost | £35 to £55 per square metre. | £55 to £85 per square metre. |
| Likelihood of membrane damage | Lower. It tends to lift away from the felt in sheets rather than bonding hard to it. | Higher. It bonds to the felt and frequently takes it with the foam on removal. |
Costs are removal and disposal only, baseline rates for England and Wales. The full 2026 breakdown by property type is on the cost page.
What your paperwork already tells you
If you have a BBA certificate, a KIWA certificate or an installer warranty from when the foam went in, it will name the product used. Most spray foam products are sold clearly as one type or the other, so this single document usually ends the question without a torch or a thumb involved. Dig it out before you do anything else, it may also carry a condensation risk assessment and thermal calculations that a surveyor will want to see later.
No obligation, no deposit
Have someone look at it properly
An hour in the loft and you will know exactly where you stand, in writing, with photographs. If the foam is sound, that is what the report says and there is nothing to pay.
Book the free inspection
Two steps. No deposit, and nothing to pay if the foam is sound.
When you genuinely cannot tell
Some lofts have been treated with more than one product, or in more than one phase, and a small number of homes genuinely have both types present in different areas of the same roof. Age, dust, and loft boarding laid directly over the foam can also make a confident call harder from a hatch.
None of that changes what happens next. An inspection settles it either way, identifies the foam type properly, checks the timbers and the ventilation, and prices the job accurately rather than off a guess. That is exactly what the inspection is for.
Identification questions
Can spray foam be a mix of open cell and closed cell?
Yes, on some roofs. It happens where the loft was treated in more than one phase, where an extension was foamed separately from the main roof, or occasionally where an installer used a closed cell skim over an open cell base. A visual check from the hatch will not always catch this. An inspection checks more than one area of the roof rather than assuming the whole loft matches one sample.
Does the colour always tell you which type it is?
No, and it is the least reliable of the checks above. Manufacturers use different pigments, and foam ages and yellows over time regardless of type. Use colour to support the thumb test, not to replace it.
Is open cell always the safer or better choice?
It is generally the easier and cheaper foam to remove and the less likely to destroy the membrane on the way out, but neither type is inherently unsafe when installed correctly with proper ventilation. The Insulation Manufacturers Association stated in February 2026 that correctly installed foam of either type is safe and rarely needs removing.
Can I tell the type from the room below without going into the loft?
Not reliably. Occasionally a very heavy, rigid feel to a boarded loft floor, or visible sagging where storage has been added over unsupported foam, hints at closed cell underneath, but this is guesswork compared to actually looking in the loft. Get into the loft, or have someone do it for you.
Why does a removal company need to know the type before quoting?
Because it changes the labour time, the likelihood of membrane replacement, and the disposal volume, all of which are priced differently. A quote given without establishing the type first is a number picked before the job has been looked at, which is exactly the kind of quote that changes once the van arrives.
Does the type of foam affect whether a mortgage lender will accept the property?
Lenders generally respond to the same underlying issue, being unable to inspect the timbers, regardless of foam type. Closed cell is more often the configuration linked to trapped moisture, which is a second and separate concern on top of inspectability. See where the lenders stand for the detail.
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