The short answer
You can usually tell the two types apart by touch. Open cell spray foam is soft, light and spongy, and it gives under a fingertip. Closed cell foam is hard, dense and rigid, and it resists pressure. The installer's invoice or product sheet is the firmest evidence, and a roofer or surveyor can confirm it from a small sample.
The touch test
The simplest check needs no tools. Press a fingertip or a thumbnail gently into the foam in a spot where a small mark will not matter. Open cell foam gives way easily, feels like a firm sponge and springs back slowly. Its surface is often rough, with a coarse, crumbly texture where it has been trimmed back.
Closed cell foam resists. It feels like a hard, tightly packed plastic, it does not squash under light pressure, and tapping it gives a dull knock instead of a soft thud. Its surface tends to look smoother and more uniform. Wear gloves and a dust mask in the loft, move along the boards only, and do not lean on anything that is not a joist.
Two details to remember. You are testing the foam, not the timber behind it. And a thin layer of closed cell foam under a thicker layer of open cell has been used in some roofs, so check more than one spot.
Thickness, colour and appearance
Look at how much foam there is. Open cell foam expands a lot as it cures, so it is usually applied thick and may fill the whole depth of the rafters, sometimes with a bulging surface that has been trimmed flush. Closed cell foam expands less and is often applied in a thinner coat that follows the rafters and leaves the timber edges visible.
Colour is a weaker guide. Foam may be white, cream, yellow or tan, and it darkens with age and dust, so the shade alone proves little. Some installers add dye. Smell is also unreliable once foam has cured.
Do not rely on one feature. Combine the touch, the depth and the finish, and treat the result as a good guess until a document or a sample confirms it. Our guide to open cell and closed cell foam sets out how each behaves in a roof, and why the difference changes what removal involves.
Paperwork that settles it
The strongest evidence is a document. Look for the installer's invoice, a product data sheet, a certificate, a quotation, or the guarantee. Any of these should name the product, and the product name will say whether it is open or closed cell. Photographs taken at installation are useful too.
If you bought a house that already had foam fitted, ask the vendor's solicitor or the seller for whatever was handed over at the time, and check the survey report from your own purchase. Some home survey reports note spray foam and describe it. Should the installer still exist, a call or email with your address and the approximate date is often enough to get a copy of the job record.
Keep what you find with the deeds. A lender, a buyer or a surveyor may all ask, and our answer on spray foam and your mortgage explains why the question comes up so often.
Why the type affects removal
Knowing the type changes the plan. Open cell is the lighter, softer product, so it tends to come away in larger pieces when cut, pulled and scraped, though it can hold moisture and sit tightly in the gaps around the timber. Closed cell foam is denser and sticks harder to what it was sprayed onto, so removal is slower and more likely to disturb the surface behind it.
That, in turn, shapes how much of the covering is at risk, how long the job runs, and how much waste there is to carry away. Costs follow from it. MyBuilder's 2026 guide gives typical UK figures of about £20 to £50 per square metre for removal, with loft area, foam type and the state of the timber behind it among the cost drivers it lists.
Removal can also be partial, and the type matters there too. Our page on partial spray foam removal looks at whether leaving some foam in place is a workable choice.
When the foam looks mixed or painted over
Some lofts do not give a clean answer. Foam may have been applied in two coats on different days, with a thin hard layer under a softer one, or one slope may have been sprayed by one firm and another by someone else. Fire-retardant or intumescent paint is sometimes brushed over the surface, which hides its true texture and colour. Dust and cobwebs can do the same.
In those cases test in several places, and brush a small patch clean before you press on it. Check the junctions with the gable walls and the eaves, where installers sometimes switched products to fill a gap. Photograph each spot and note where it is, because the pattern across the roof is useful to whoever works on it later.
If the results vary from one slope to another, say so to anyone who quotes. A removal plan for a mixed roof is not a single price per square metre, and the quote should reflect what is really there.
When to ask someone to look
If the touch test and the paperwork disagree, or the foam is a mix of textures, have it looked at. A roofer who knows the product can often identify it on sight, and a small sample cut from an unobtrusive area can be checked against manufacturers' descriptions. Removing a sample does not need to disturb the roof, and it avoids guessing.
During our free survey we study the foam, take pictures of your own loft, and record the type, the depth and the state of the timber side by side. Season has little effect on this stage, and our answer on removing spray foam in winter shows how the rest of the job is timed. Call 01225 285181 or use WhatsApp to arrange it. The spray foam insulation hub lists the other questions we answer.
