18th Nov 2022 -

Fire-resistant insulation is available in many forms for use throughout a range of building projects. There is a general rating system by which all insulation can be tested, with options available that are fully non-combustible. While some types of insulation will be resistant to extreme temperatures, and non-combustible, none of them will ever be entirely fireproof.

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Is Fireproof Insulation Possible?

Fully fireproof insulation is not possible, and fire-resistant or fire-rated is a more accurate term in most cases. There are a wide variety of insulation options that will not combust, and that can withstand high temperatures. Preventing the passage of smoke and flames is also important. Within contemporary buildings, there are strict rules about the use of fire-resistant insulation, particularly in larger buildings like tower blocks.

How Is Fireproof Insulation Tested?

Insulation products can be assessed via British Standard (BS) backed tests. These will determine the combustibility of thermal insulation, the smoke emissions during combustion, and the levels of flaming particles produced during construction. In addition to these tests, products can opt for a class 0 or class 1 rating, which is a more limited test of surface fire performance. Compared to the more elaborate British Standard classification system, the class 0 and class 1 ratings are not considered authoritative.


Combustibility is the tendency of a material to burn due to a fire or a chemical reaction. A flammable substance is one that easily catches fire, while a combustible one will be more difficult to ignite and may not burn as strongly. Below are the British Standard classifications for products. When looking for fire-resistant thermal insulation you would be looking for fire-rated products with an A1 or A2 classification. Lower-rated products will sometimes contribute to the spread of flames, catching on fire in extreme circumstances.

A1Non-combustible, will not contribute to a fire
A2Non-combustible, but with potential for some smoke or flaming particles
Class BVery limited contribution to a fire
Class CLimited contribution to a fire
Class DMedium contribution to a fire
Class EHigh contribution to a fire
Class FEasily flammable

Smoke Emission During Construction

All products are also rated on the smoke emissions that occur during combustion. Below are the British Standard classifications a thermal insulation product can achieve.

S1Low levels of or no smoke emission
S2Medium levels of smoke emission
S3High levels of smoke emission

Flaming Particle Production

Flaming particles, sometimes called flaming droplets, can drip from insulation, causing a health risk during building evacuation. British standards classify flaming particle production by three standards.

D0No drips
D1Slow dripping
D2High dripping

Which Insulation Materials Are Fire Resistant?

Some of the common insulation materials are naturally fire-resistant, while others can be sprayed in a fire-resistant coating to improve their fire performance.

Mineral Wool

Mineral wool products, both rock wool and slag wool varieties, are non-combustible, meaning they will not contribute to the spread of a fire. Mineral wool also has a high melting point, withstanding temperatures up to about 1100°c. Seeing as the average house fire will top out at around 750°c this means that it is unlikely to burn or degrade in most fires, making it an excellent choice for safety. Mineral wool is sometimes faced with paper or other materials, which can be flammable.


Fibreglass insulation is also non-combustible, meaning it will not contribute to a fire. However, it has a lower melting point, at around 540°c, meaning it could melt during an intense house fire, allowing flames to spread to other flammable materials within the construction. Sometimes Fibreglass is faced with a layer of kraft paper or a vapour barrier, which may be flammable.

PIR Insulation

PIR insulation boards are a wholly manufactured product, so they won’t have specific generalised fire values. As such, there will be PIR products with lower fire ratings, such as the Celotex TB4000 which has an E rating, and products that rate much higher, like the Kingspan K110 Plus Soffit Board which has a B rating. PIR insulation can release toxic smoke when combusted. If looking to use PIR insulation within a building, you should carefully check its fire rating during the planning process.

Foam Insulation

While blown-in cellulose insulation can have a low resistance to fire despite being sprayed with a flame retardant, other types of spray foam can offer better protection. Like PIR, you should seek out a fire-resistant foam insulation option if needed.

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Best Fire Resistant Thermal Insulation 

When looking to install fire-resistant insulation within a property, alongside other methods of fire protection you should seek to use mineral wool or fibreglass products. These are available for use throughout most of a building.

Best Fire Resistant Loft Insulation

Using mineral wool rolls or batts within the joists of a loft can offer fire resistance as well as thermal insulation. Mineral wool products will be non-combustible and resistant to melting and the passage of fire. For fire-resistant roof insulation, you will also be able to use solid mineral wool batts.

Best Fire Resistant Wall Insulation

Within a stud wall, fire-retardant mineral wool batts can be used. You may want to opt for metal studs instead of wooden ones to further improve the fire resistance offered by your internal wall. In a new build, mineral wool batts are available for cavity wall insulation. Other insulation materials will not offer the same level of fire resistance.

Our Excellent Range of Insulation

Building Materials Nationwide stocks a huge selection of thermal insulation. If you are looking for fire-rated products, you’ll find a range of mineral wool and fibreglass insulation products, for installation within lofts, internal walls, and cavity walls. These will reduce heat loss and increase the energy efficiency of a home. We prioritise taking the hassle out of sourcing building supplies, with a comprehensive product range, express nationwide delivery and competitive pricing on all products. We offer trade accounts for our customers in the industry, opening up even more benefits.

Sign up for a trade account through our website today, or submit your query through the form below. A member of our friendly team will guide you in choosing the right fire-resistant insulation for your building project.

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