Wall Insulation Materials - Wall Insulation

Choosing the right wall insulation materials is one of the most important decisions you will make in any home energy improvement project. The material you choose affects how well your walls perform thermally, how much internal space you lose, how the finished surfaces look, and how long the insulation lasts. Because every property is different, there is no single answer that works for every home.

This guide explains the main wall insulation materials used across the UK in 2026, how they compare, and what you should consider when deciding which one is right for your property.

Why the Choice of Wall Insulation Materials Matters

Wall insulation materials are not interchangeable. A product that works brilliantly in one context can be poorly suited to another. For example, a material with excellent thermal performance but poor moisture resistance would be a bad choice for a wall with known damp issues. Similarly, a bulky material that requires a thick installation might be impractical for an internal retrofit where space is at a premium.

Understanding the characteristics of each material helps you have a more informed conversation with your installer and avoid costly mistakes.

Mineral Wool

Mineral wool is one of the most widely used wall insulation materials in the UK. It comes in two main forms: glass wool, made from recycled glass fibres, and rock wool (also called stone wool), made from volcanic basalt rock. Both are available as flexible batts or semi-rigid slabs.

Mineral wool is non-combustible, which gives it a significant fire performance advantage over foam-based products. It also performs well acoustically, making it a popular choice for party walls and internal partitions where sound transmission is a concern.

In terms of thermal performance, mineral wool has a lambda value typically around 0.032 to 0.044 W/mK depending on density. This means it requires a moderate thickness to achieve good thermal resistance. For internal wall insulation, it is usually used within a studwork or framing system rather than bonded directly to the wall face.

Mineral wool is generally considered a breathable material, which makes it a reasonable choice for older properties where some moisture movement through the wall structure is desirable.

PIR (Polyisocyanurate) Board

PIR is a rigid foam board product and one of the most thermally efficient wall insulation materials available for retrofit projects. It has a lambda value typically around 0.022 to 0.028 W/mK, which means it delivers excellent thermal resistance in a much thinner profile than mineral wool.

Because PIR board can achieve the required U-value with less thickness, it is particularly popular for internal wall insulation where preserving floor area is a priority. It is bonded directly to the wall or installed within a slim battened frame and then boarded over with plasterboard.

PIR is not breathable in the way mineral wool is, so it is important that any installation includes appropriate vapour control detailing to avoid interstitial condensation within the wall build-up. A good installer will assess this as part of the specification.

EPS (Expanded Polystyrene) Board

EPS board is a lighter and more affordable rigid foam option. It has a lambda value typically around 0.031 to 0.038 W/mK, which sits between mineral wool and PIR in terms of thermal efficiency. EPS is widely used in external wall insulation systems, where it is fixed to the outside face of the wall and covered with a render or cladding finish.

EPS is moisture resistant and dimensionally stable, which makes it well suited to external applications. It is also available in very large sheet sizes, which makes it efficient to install on flat wall elevations. On the downside, it requires more thickness than PIR to achieve the same thermal performance.

Phenolic Foam Board

Phenolic foam board offers the highest thermal performance of any mainstream rigid wall insulation material. With a lambda value typically around 0.018 to 0.023 W/mK, it achieves very high levels of thermal resistance in an extremely slim profile.

It is more expensive than PIR or EPS, but in situations where wall space is genuinely critical, the additional cost is often justified. Phenolic board is most commonly used in high-specification internal wall insulation projects.

Urea Formaldehyde Foam

This material was used extensively for cavity wall insulation in the 1970s and 1980s and is now banned for new installations. If your home was insulated before 1990, there is a possibility this material was used. It is known to shrink and crack over time, leaving gaps in the insulation and in some cases releasing formaldehyde vapour into the home. If you suspect this material is present, arrange a professional inspection.

Aerogel Insulation

Aerogel is an advanced insulating material with exceptionally low thermal conductivity, typically around 0.015 W/mK. It is available as flexible blanket products or bonded panels and is used in situations where even phenolic board is too thick, such as listed buildings or properties with very limited internal space.

The main drawback is cost. Aerogel products are significantly more expensive than conventional wall insulation materials and are generally reserved for specialist or heritage applications.

How to Choose the Right Material for Your Home

The right choice of wall insulation materials depends on several factors:

Wall construction: solid wall properties typically use internal or external rigid board systems, while cavity wall properties use blown or injected fill materials. The material must suit the construction type.
Space constraints: if you are insulating internally and cannot afford to lose much floor space, higher performing thinner materials such as PIR or phenolic foam are worth the additional cost.
Moisture and breathability: older properties with lime mortar construction or known moisture issues may benefit from breathable materials such as mineral wool or specialist breathable boards. A surveyor can assess this during an initial inspection.
Budget: mineral wool and EPS are generally the most cost-effective options. PIR sits in the middle ground. Phenolic and aerogel are premium products for specific applications.
Fire performance: if fire resistance is a priority, non-combustible mineral wool has an inherent advantage over foam-based products.

Why Summer 2026 Is the Right Time to Choose and Install

After a remarkably warm and dry spring, conditions are ideal for starting an internal or external wall insulation project. Dry weather reduces moisture risk during installation, and with a full summer ahead, any external render systems have optimal conditions to cure properly. Booking now also helps you avoid the autumn rush when demand for qualified installers typically peaks.

For detail on rigid board options specifically, see our guide to wall insulation board. If you are thinking about cavity wall insulation and wondering how long it lasts, our dedicated guide covers the key questions.

If you are considering external wall insulation as your chosen approach, ecoinsulation.co.uk covers external systems in detail, including costs, materials, and available grants for 2026.

Take the Next Step

If you are ready to choose wall insulation materials for your home, the best starting point is a professional survey. A qualified installer will assess your wall construction, measure up, and recommend the most suitable material and system for your specific property. Contact us today and take advantage of the spring installation window before the summer books up.

No fines concrete construction is one of the most misunderstood and most problematic types of wall insulation when it comes to insulation. If your property was built between the 1940s and 1970s, particularly through a local authority housing programme, there is a meaningful chance it uses no fines concrete. Standard cavity wall insulation systems do not apply here, and applying the wrong treatment can cause serious and expensive problems. This guide explains what no fines concrete is, why it behaves differently from brick construction, and what your options actually are.

What Is No Fines Concrete?

No fines concrete is a construction method that uses coarse aggregate and cement but deliberately excludes the fine sand particles that give standard concrete its density. The result is a porous, open textured material full of interconnected voids. Walls built from no fines concrete are typically cast in a single leaf, around 230 to 250mm thick, with no cavity. The types of wall insulation here is different.

The method was popular in post war local authority housing programmes because it was fast to construct using shuttered formwork systems. Entire estates of identical properties were built using no fines concrete across Scotland, the north of England, and parts of Wales and the Midlands. Many of these properties are now in private ownership following the right to buy programme.

You can often identify no fines concrete from the outside by the distinctive dimpled, open textured render that covers the structural wall. Inside, the walls feel dense and cold to the touch but lack the smooth, regular surface of a plastered brick wall.

Why Standard Insulation Does Not Apply

No fines concrete walls present two specific challenges that make standard insulation approaches inappropriate or risky.

No Cavity

No fines concrete construction uses a single leaf wall with no cavity. Cavity wall insulation, the cheapest and most common form of wall insulation in the UK, simply does not apply. There is nothing to fill.

The Porosity Problem

Not all types of wall insulation are the same. The open, voided structure of no fines concrete means the wall absorbs and transmits moisture in a way that dense brick does not. Rain penetrates the outer face, travels through the voids in the concrete, and exits at the inner face. In an unmodified no fines concrete wall, this is managed by the original render coat on the outside, which is designed to be the primary weather barrier.

Any insulation system applied to a no fines concrete wall must either maintain this weather barrier function or replace it entirely. A system that compromises the weather barrier without providing an equivalent replacement will drive moisture inward.

This is the core reason why some insulation treatments that work well on brick properties fail badly on no fines concrete.

What Happens When the Wrong Types of Wall Insulation Are Used

The failure mode most commonly associated with poorly specified insulation on no fines concrete is internal damp following the injection of cavity wall insulation into properties that do not actually have a cavity, or that have a void in the render coat that gets filled without addressing the underlying structure.

Some no fines concrete properties were incorrectly assessed as cavity wall construction during large scale insulation programmes in the 1980s and 1990s. Insulation material was injected into the wall but, because the wall is solid porous concrete rather than a true cavity, the material bridged moisture pathways rather than filling a discrete void. Persistent internal damp followed in a proportion of these cases.

If your no fines concrete property had insulation injected and you subsequently experienced damp problems, this is the most likely explanation.

The Right Options for No Fines Concrete – Types of Wall Insulation

External Wall Insulation

EWI is generally the recommended solution for no fines concrete properties. Applied correctly, it provides a new weather barrier on the outside of the building, eliminates moisture ingress through the original porous structure, and delivers a substantial improvement in thermal performance.

The critical requirement is that the EWI system includes a continuous, weather resistant render or cladding finish that replaces the function of the original render coat. The system also needs to be breathable enough to allow any residual moisture in the concrete structure to escape outward during dry periods.

Woodfibre or mineral wool insulation boards are often preferred over EPS on no fines concrete because they are more vapour permeable, which supports the moisture management of the underlying wall. The finish coat should be a silicone or mineral render with good vapour permeability.

The substrate assessment is particularly important on no fines concrete. The pullout strength of mechanical fixings into porous concrete differs from that in dense brick, and the installer needs to test this before specifying the fixing pattern.

Internal Wall Insulation

Internal wall insulation is possible on no fines concrete but requires careful attention to vapour control. The insulation must include a vapour control layer on the warm side to prevent moisture from the room air condensing within the wall construction. Without this, interstitial condensation can occur at the cold, porous concrete surface behind the insulation.

Internal insulation on no fines concrete works best with a breathable insulation system, woodfibre or hemp, combined with a correctly positioned vapour control layer. Rigid closed cell insulation boards applied directly to the concrete face without adequate vapour control have a higher risk of moisture problems.

Internal insulation also reduces the internal floor area and requires repositioning skirting boards, radiators, electrical sockets, and window reveals, a significant disruption compared to EWI.

Solid Wall Insulation Through Government Schemes

No fines concrete properties are eligible for solid wall insulation funding through ECO4 and the Great British Insulation Scheme, provided the household meets the eligibility criteria. An installer who understands no fines concrete construction should be able to assess the property and confirm eligibility.

The key is finding an installer with specific experience in this construction type. Not all PAS 2030 certified installers have worked on no fines concrete, and the specification needs to come from someone who understands its particular moisture management requirements.

Finding Out If Your Property Is No Fines Concrete

If you are not certain whether your property uses no fines concrete construction, several checks help:

Build date and type. Properties built between 1945 and 1975 through local authority programmes in Scotland, the north of England, and Wales have a higher probability of no fines concrete construction.

External appearance. The original render on no fines concrete properties has a distinctive dimpled, coarse textured appearance that differs from sand and cement render on brick.

Local authority records. If the property was originally council owned, the local authority may have construction records. These are not always accessible to private owners but are worth requesting.

Professional survey. A building surveyor can identify no fines concrete from an inspection and confirm the wall construction type. This survey is worth commissioning before any insulation work to ensure the system is correctly specified.

Frequently Asked Questions About Types of Wall Insulation

Can I get free insulation for a no fines concrete house? Possibly. No fines concrete properties are eligible for solid wall insulation funding through ECO4 and GBIS if the household meets the eligibility criteria. Contact a TrustMark registered installer to run an eligibility check for all types of wall insulation.

Why did my no fines concrete house develop damp after insulation was installed? The most likely cause is that cavity wall insulation was injected into a wall that either had no true cavity or had the insulation material penetrate the porous structure in a way that bridged moisture pathways. If this has happened, a specialist survey is needed to diagnose the extent of the problem before deciding on remedial action and choosing between types of wall insulation.

Is EWI always the best option for no fines concrete? It is generally the preferred option because it addresses the weather barrier function of the original render and eliminates moisture ingress from outside. Internal insulation is technically possible but requires more careful specification and carries a higher risk if the vapour control is not correct.

Do I need planning permission for EWI on a no fines concrete house? The planning rules for EWI on no fines concrete houses are the same as for brick properties. Permitted development rights cover EWI for most houses in England, but conservation areas and listed buildings require specific consent. Check with your local planning authority if you are in a sensitive location for different types of wall insulation.

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Information correct as of April 2026. Always commission a professional survey to confirm wall construction type before specifying any insulation system for a no fines concrete property.

Wall Insulation Materials Explained: Which Option Works Best for UK Homes in 2026