Can You Use Expanding Foam for Fire Stopping? A Guide for Facilities Managers
TL;DR
Ordinary expanding foam is not a fire seal. It is a combustible filler and can help fire and smoke through the wall it was meant to protect.
Some foams are sold as "fire rated", but that label often describes how the foam reacts to flame, not how long it holds back a fire.
A foam can only be used where the manufacturer has test evidence for that gap size, that wall or floor and that service, and it is fitted exactly as tested.
Most cable bundles, plastic pipes and large holes need a different tested product, such as a collar, wrap, batt or intumescent sealant.
If you find foam in a fire-resisting wall and have no record of what it is, treat it as a defect and get it checked as part of fire stopping work.
Lift a ceiling tile next to a riser or a comms room in almost any building and there is a good chance you will find it: a hole round a cable tray or pipe, filled with a puff of pink or grey foam and trimmed flush. It looks sealed. The question an auditor will ask is whether it would still be sealed after 30 or 60 minutes of fire, and for most foam you will find above a ceiling, the honest answer is that nobody knows.
Can you use expanding foam for fire stopping?
Only in limited cases. A foam can form part of a fire seal when it is a fire-rated product with test evidence for the exact situation: the gap width and depth, the wall or floor type, the service passing through and the fire resistance period needed. Fitted outside that evidence, or if it is ordinary builders' foam, it is not fire stopping, however neat it looks.
Is expanding foam fire rated?
Standard polyurethane foam is not. It is made to fill gaps and insulate, and it will burn. Fire-rated foams exist, often coloured pink, and are formulated to resist flame. But colour proves nothing: some pink foam is not fire rated, and some fire-rated foam is not pink. The only way to know is the product name on the can, its data sheet and the test evidence behind it. Our article on how intumescent fire stopping products work explains how proper seals behave in a fire.
What is the difference between B1, B2 and fire resistance?
B1 and B2 are reaction to fire classes from the German standard DIN 4102. They describe how readily a material catches and spreads flame. They do not tell you how long a sealed gap will stop fire and smoke passing through a wall. That is fire resistance, shown as an EI rating in minutes (for example EI 60) and proved by testing the seal in a wall or floor. For a compartment wall, fire resistance is what counts, so a "B1 foam" label on its own is not enough.
When can fire-rated foam be used?
Fire-rated foam is usually tested for narrow linear gaps, such as the joint around a door or window frame or between wall panels, within set widths and depths and in set substrates. Some products also have evidence for certain small service penetrations. Anything outside the manufacturer's tested details, such as a wider gap, a different wall or a service it was not tested with, is not covered. Check the data sheet and keep a copy with your records.
Where should you not use expanding foam?
The everyday places foam turns up where it should not:
Around plastic pipes. Plastic softens and collapses in a fire, leaving an open hole. These normally need an intumescent collar or wrap. Our article on fire stopping pipe penetrations covers the usual solutions.
Through cable bundles and trays. Foam rarely fills between cables and is seldom tested for them. See our article on fire stopping around electrical cable penetrations.
Large holes left after old services are removed, often patched with a whole can of foam.
Holes made after the original work, for example new data cables or a new heating pipe run through a riser wall during a fit-out.
The gap between a fire door frame and the wall, unless the door's own installation instructions allow that product.
Anywhere near heat sources such as flues and chimneys, where non-combustible products are needed.
Why is foam above ceilings such a common problem?
Because it is quick, easy to carry and easy to use, and because ceiling voids and risers are rarely looked at once a job is finished. Every trade that runs a new cable, pipe or duct through a fire-resisting wall makes a new hole. If the follow-up seal is a can of foam rather than a tested product, the wall loses its fire resistance at that point. Our article on passive fire protection failures found after refurbishments shows how often this happens, and a missing cavity barrier above a ceiling is a related defect in the same voids.
How can you tell if foam in a wall is acceptable?
Ask four questions about each sealed opening:
Do you know the product? A name, a data sheet, or an empty can left on site is a start. Unknown foam should be treated as unproven.
Is there test evidence for this use? The gap size, wall or floor type and service must match the manufacturer's tested details.
Was it fitted as tested? Full depth, no voids, the right backing material where specified, and not trimmed back into the hole.
Is it recorded? Location, product, installer, date and photographs, ideally with a label on the seal.
If the answer to any of these is no, the opening needs inspecting and is likely to need remediation. Our article on what fire stopping is and how you know if it has failed covers the wider signs.
What should replace foam that is not compliant?
The foam is cut out and the opening resealed with a product tested for that situation, such as intumescent sealant, fire batt and mastic, pipe collars or wraps, or a tested foam within its limits. Each seal is then photographed and recorded so the next audit, or the next contractor, can see what is there. This is the core of fire stopping remediation, and on a larger estate it is usually found and planned through a fire compartmentation survey.
What to do next: how Protest ES Ltd helps
Protest ES Ltd works with facilities managers, managing agents and FM providers across commercial, education, healthcare and public sector estates. We don't simply identify compliance issues. We help clients close them:
Fire stopping surveys that open up ceilings and risers, record every penetration with photographs and identify unproven foam and open holes
Fire stopping remediation that removes non-compliant foam and reseals each opening with a tested product, with a record for every seal
Fire compartmentation surveys that check the walls and floors your fire strategy relies on, room by room and floor by floor
Passive fire protection advice on what to fix first, so the highest-risk openings are closed before the next audit
One visit, more disciplines. Most FMs use separate contractors for fire doors, fire stopping and electrical testing, each with its own access, programme and paperwork. Protest ES Ltd delivers passive fire protection, including fire stopping and fire compartmentation, fire door remedials and electrical compliance on the same visit: one contractor, one programme, one set of records across every site.
If you have found foam in your ceiling voids or risers and are not sure what it is, get in touch with our team or visit Protest ES Ltd.
Further reading from Protest ES Ltd
How Often Should Fire Stopping Be Inspected in a Commercial Building?
What Is a Fire Compartmentation Survey and How Often Should One Be Done?
What Is a Passive Fire Protection Survey and What Does It Cover?
Fire Stopping Around Electrical Cable Penetrations Explained
Common Passive Fire Protection Failures Found After Refurbishments
Frequently asked questions
Is pink expanding foam fire rated?
Not necessarily. Pink is a common colour for fire-rated foam, but colour is not a rating and some pink foams are not fire rated at all. Check the product name, data sheet and test evidence. Without them, treat the foam as unproven.
Is fire-rated foam the same as fire stopping?
No. Fire-rated foam is one product that can form a fire seal in the situations it was tested for. Fire stopping is the whole job of sealing gaps and service penetrations so a fire-resisting wall or floor keeps its rating, using whichever tested product fits each opening.
Where should you not use expanding foam?
Around plastic pipes, through cable bundles, in large holes, near flues and in any fire-resisting wall or floor where the foam has no test evidence for that use. In those places a collar, wrap, batt, intumescent sealant or other tested product is needed.
What does B1 mean on expanding foam?
B1 is a reaction to fire class from the German standard DIN 4102, meaning the material is hard to ignite. It does not show how long a sealed gap will resist fire. For a compartment wall you need fire resistance evidence, shown as an EI rating in minutes, for the way the foam is being used.
Can you fire stop around cables with foam?
Rarely. Foam does not fill reliably between cables and few foams are tested for cable penetrations. Cables through fire-resisting walls are usually sealed with intumescent sealant, batt and mastic, or a tested cable system, fitted to the manufacturer's details.
Who is responsible for fire stopping in a building?
The responsible person under the Regulatory Reform (Fire Safety) Order 2005, which in practice often sits with the facilities manager or managing agent. They should make sure penetrations are sealed with suitable products, recorded and checked, especially after any work that runs new services through fire-resisting walls.
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