Anyone sorting out a foamed roof soon hears the two terms. A surveyor's note may say "closed-cell foam to the underside of the slope", an installer's old paperwork may say "open-cell", and a buyer may have neither. The words describe how the foam is built at a microscopic level: whether the tiny bubbles in it are sealed shut or connected to one another. That structure shapes how firm the foam is, how it handles moisture and how it behaves when someone needs to inspect or remove it.
It matters for a roof in two ways. The first is risk. The Energy Saving Trust does not recommend foaming a roof that is already damaged, with the fault left unrepaired, and adds that the risk should be much lower with an open-cell foam. The second is practicality: the type affects what a surveyor can learn from the loft, what a lender wants to see and how the foam is removed.
We are roofers, not insulation manufacturers, so this page stays on what we see on site. Performance figures belong on the product's own data sheet and vary from product to product, so you will not find them here. If the foam in your roof is already causing worry, our spray foam insulation removal service begins with working out which kind you have.
What the two names actually mean
Both kinds start as liquids that are sprayed onto a surface, then expand and set into a solid. The installer's gun mixes the chemicals as they leave the nozzle, and what the foam ends up like depends on the mix and the conditions on the day. The difference lies in the cells, the small pockets of gas that make up the foam. In closed-cell foam, the cells are sealed, which tends to make the finished material dense, firm and rigid. In open-cell foam, the cells are connected, which usually leaves it lighter, softer and more like a sponge.
That one distinction carries a chain of effects. A firm foam sticks hard to what it is sprayed on and can add stiffness to the surface. A soft foam grips less hard and gives under pressure. A closed structure tends to resist the passage of water and vapour more strongly than an open one, although how much depends on the product, its thickness and how well it was installed. We cannot quote a figure for your foam, and nobody should without seeing the data sheet or testing.
Why the label alone is not enough
Installers, brochures and sales teams do not always use the terms consistently, and some products sit between the two descriptions. A roof can also have been done in two passes with different products, or been topped up years later. So we treat any label as a lead to follow up, not as a fact, and confirm what is up there with our own eyes.
What the RICS consumer guide stresses is the risk of damp where foam is incorrectly installed, and nothing in that warning is limited to one kind. Our page on what RICS says about spray foam insulation goes through the guide in full.
Why the Energy Saving Trust sees lower risk with open cell
The Energy Saving Trust, in its roof and loft insulation advice last updated in May 2026, makes a specific warning. It says some companies offer to fix a damaged or leaking roof by spraying foam onto the underside without dealing with the underlying fault, and it does not recommend doing this. It then says the risk should be much lower with an open-cell foam.
Read carefully, that is a statement about concealment. If foam is sprayed over a leak, the water still comes in. What changes is whether anyone can see it. A foam that blocks the view and also keeps water against the timbers can let a small fault turn into a rotten rafter without a single stain on the ceiling. By the time a mark shows, the damage may be well advanced. A softer, more open foam leaves more chance that water shows itself, or dries, so the same fault is less likely to go unnoticed. The Trust does not say open-cell foam is risk-free, and neither do we.
What this means if you have closed-cell foam
It does not mean closed-cell foam is a problem in itself. A roof whose covering is sound, whose ventilation and detailing were considered and whose timbers are dry may do very well with either kind. What it does mean is that, with closed-cell foam over a roof of unknown condition, the stakes of an undiscovered fault are higher. That is a reason to check, not to panic.
If you are buying or selling, expect a surveyor to ask which type is installed, and expect a lender to ask the surveyor. Our guide to spray foam roof damage describes the faults that tend to appear behind either kind.
How to tell which kind is in your roof
Start with paperwork, because it costs nothing to collect. An installer's invoice, a guarantee, a data sheet or a survey from the time of installation may name the product. If the work was funded through a scheme or a supplier, the records might sit with them. A previous owner's solicitor may hold copies. It costs nothing to ask before any visit.
Without paperwork, a loft inspection gives strong hints. Closed-cell foam is generally hard, resists a thumb pressed against it and may sound firm if tapped. Open-cell foam is typically softer, gives under finger pressure and has a coarser, more crumbly look when cut or torn. Colour is not reliable, since manufacturers use different shades for both. Thickness can also point one way or the other, but the hints are not proof.
Do not dig into the foam to find out. Breaking the surface in a roof you plan to sell or insure can create problems of its own, and the edge you expose may be harder to put back. A surveyor can take a small, discreet sample from a place that will not be noticed, if one is needed at all. Photographs of the foam's face and its edges, taken with a scale reference, are usually enough for an informed opinion.
What to do with the answer
Write the type down, with the date you found out and how. Add it to whatever file you keep for the property, and give a copy to your solicitor if a sale is on the horizon. A lender who is asking questions about the foam will want the answer, and having it ready shortens the conversation. Our guide to spray foam insulation and mortgages sets out which questions tend to follow.
Closed-cell foam on a roof: the particular concerns
Closed-cell foam tends to be the harder one to live with if the roof turns out to need work. It bonds firmly to the underlay, the battens and the rafters, so inspecting what lies behind it is difficult without cutting through. It can also make a developing fault harder to read from inside, since a firm layer masks the small signs a bare rafter would show.
The covering is the other concern. Foam in contact with the back of tiles or slates can make it difficult to lift one for a repair without disturbing the foam, and a cracked or slipped tile above closed-cell foam may let water in with nowhere to go. We look carefully from outside for slipped, cracked or loose coverings on a foamed roof, because a repair here is cheaper than a repair after the timbers behind have been wet for a winter.
If it must come out
Firmer foam usually means a slower, more careful removal, because the foam grips the timbers and each section has to be released without tearing them. The RICS guide says removal could potentially damage the existing structure, and with a dense, well-stuck layer that caution carries more weight. Our guide to how spray foam insulation is removed sets out the stages, and the time and cost differ with the foam and the access, which the survey settles.
If the foam is sound, the timbers are dry and the lender and surveyor are comfortable, leaving it alone is a legitimate choice. If that is what the survey finds, that is what we put in the report: the smallest job that properly deals with what is there.
Open-cell foam on a roof: the particular concerns
Open-cell foam has its own concerns, and the Energy Saving Trust's comment on lower risk should not be read as a clean bill of health. A softer foam is not the same as an absent one. It still covers the timbers, it still hides the underside of the covering and it can still hold moisture against the wood if the conditions are right. A sensible survey checks the edges and the covering in exactly the same way.
Condensation is the other thing to bear in mind. Foam changes how a roof manages moisture from the house, and the question of whether a given product and thickness are right for a given roof is the one that RICS says needs thermal calculations and condensation risk checks by a qualified professional. That applies whichever kind was installed. Our short answer on re-roofing over spray foam explains why this matters when the covering has to be replaced.
Removal and re-roofing
With softer foam, removal can be more forgiving, since the foam grips less hard and may release in larger pieces. That does not make it a quick job: the timbers still need to be checked once exposed, and a membrane and ventilation still need to go back. In a re-roof, the foam usually has to be dealt with before or during the stripping of the old covering, as the two jobs affect each other.
Equity release and later lending are separate questions, but they are worth knowing about early. Our guide to spray foam and equity release covers how lenders in that market have approached the subject, and knowing the type in advance saves time.
Whichever foam is up there, the sequence we follow is the same. We look at the roof's condition first, then at what the owner wants from the building, and only then at whether the foam stays or goes. Starting from the answer, whether that is "strip it all out" or "leave it be", tends to produce the wrong job. Starting from the evidence rarely does.
