Pink Expanding Foam — Can I Use It as Fire Stopping?
It's in every builders' merchant, it seals gaps perfectly, and it comes in pink so it looks like it could be the right product. But using standard expanding foam as fire stopping is one of the most common — and potentially fatal — mistakes made in construction and refurbishment.
The Short Answer: No
Standard pink (or any colour) expanding polyurethane foam is not a fire stopping product. It has no fire resistance rating. In a fire, it melts and burns, actively assisting the spread of flames and toxic smoke through the very gaps it was used to fill.
Why Is This Mistake So Common?
Pink expanding foam is used extensively in construction because it is inexpensive, easy to apply and excellent at sealing gaps around pipes, cables and conduits from a draught and acoustic perspective.
The pink colour was originally used by some manufacturers to differentiate their products, and over time it became associated in tradespeople's minds with being a "specialist" product. Some also confuse it with intumescent expanding foam, which is a completely different product. The result is that pink foam is routinely found in buildings during fire stopping audits — used in precisely the locations where proper fire stopping is most critical.
What Happens to Expanding Foam in a Fire?
Standard polyurethane expanding foam has an ignition temperature of around 310°C and a flash point of approximately 240°C. In a structural fire, temperatures in a room can reach 600°C or more within five minutes of flashover.
When exposed to heat, polyurethane foam:
- Begins to soften and deform at relatively low temperatures
- Releases highly toxic gases including hydrogen cyanide and carbon monoxide
- Ignites and burns, providing additional fuel to the fire
- Melts away entirely, leaving the penetration it was filling completely open
The opposite of what a fire stop should do. A properly installed fire stopping product seals the penetration more effectively the hotter the fire gets.
What Is Fire Compartmentation and Why Does It Matter?
Buildings are designed with fire compartments — sections of the building divided by fire-rated walls, floors and ceilings. The purpose of compartmentation is to contain a fire within the compartment where it starts, slowing its spread and giving occupants time to evacuate safely.
Every time a pipe, cable, duct or conduit passes through a fire-rated wall or floor — what's known as a penetration — it creates a weak point in that compartment. Without proper fire stopping, a fire that breaks through one of those penetrations can move rapidly to other parts of the building.
Effective fire stopping restores the integrity of the fire compartment at every penetration point. It must be tested, certified and installed by competent persons using the correct products for the specific substrate and service type.
Has Your Building Been Fire Stopped Correctly?
We identify and remediate substandard fire stopping across London and the South East.
What Should Be Used Instead?
The correct product depends on the type of penetration, the service passing through, and the fire rating required. All fire stopping products must have a tested and documented system — you cannot simply use a certified product in any way you choose. It must be installed strictly in accordance with the manufacturer's tested and approved system data sheet.
Intumescent Fire Stopping Foam
Specifically formulated to expand significantly when exposed to heat, sealing the penetration. Not to be confused with standard polyurethane foam — always check the product data sheet for a fire resistance rating and tested system reference.
Intumescent Collars and Wraps
Used around plastic pipes passing through fire-rated elements. When heat reaches the collar, it crushes inward, sealing the melting pipe and preventing fire spread through the penetration.
Intumescent Fire Stopping Sealant
A flexible sealant used for gaps and joints in fire-rated constructions. Available in various grades to suit different gap sizes and substrates.
Fire Stopping Boards and Pillows
Used in larger openings and cable trays. Highly effective and easy to reopen for future cable additions.
Fire Mortar
A cementitious product used to reinstate the full fire resistance of a wall or floor around large penetrations and service ducts.
The Legal Position
Under the Regulatory Reform (Fire Safety) Order 2005, the responsible person for any non-domestic building is legally obliged to ensure that fire compartmentation is maintained. This includes all penetration seals. Using a non-rated product — even if unknowingly — does not provide a defence.
Following the Grenfell Tower fire and the Hackitt Review, there is heightened regulatory scrutiny on fire stopping quality in all building types. The Building Safety Act 2022 extended these duties and introduced the Building Safety Regulator, with particular focus on higher-risk residential buildings (those of 18 metres or more, or seven or more storeys).
Found Expanding Foam in Your Building?
If a survey or inspection has identified standard expanding foam used as fire stopping in your building, it should be treated as a defect requiring prompt remediation. The foam must be removed and replaced with an appropriate, tested fire stopping system. Do not simply apply fire stopping product over the top of the foam — it must be properly removed first.
How to Identify the Difference
Standard Expanding Foam (NOT fire rated)
- • Marketed for insulation, draught-proofing, gap-filling
- • No fire resistance classification on the label
- • No system data sheet with fire test evidence
- • Yellow, off-white, grey or pink once cured
- • Examples: standard PU foam from any builders' merchant
Intumescent Fire Stopping Foam (Fire rated)
- • Specifically marketed for passive fire protection
- • EI or REI classification on the label
- • Comes with tested system data sheet
- • May be red, pink or branded colour
- • Examples: Hilti FS-ONE, Rockwool FirePro, STI Pensil
Get Your Fire Stopping Audited by Experts
Fyrup carries out fire stopping surveys and remediation work across London. We identify substandard installations, provide a full written report and restore compartmentation to code.