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Different types of cavity wall insulation… and their pros and cons!

Different types of cavity wall insulation

Are you thinking of cavity wall insulation? Do you want to know which insulation materials are the best for your home? Or are you trying to better your knowledge on the current insulation inside your cavity walls to decide if it’s time for an upgrade? Look no further! Here, in this article, you will be provided with an accurate breakdown of the different types of cavity wall insulation and their pros and cons, all from the mouths of our trained cavity wall insulation specialists here at First Choice Energy Ltd.

Does your home have a cavity wall? Yes? If so, it is extremely important for you to know what materials it is insulated with and what kind of insulation is best for it, or if cavity wall insulation is even appropriate at all for your home (see our article Is my home suitable for cavity wall insulation? ).

A quick overview on cavity wall insulation and if its appropriate for your home

Given all the correct boxes are ticked for your home, i.e., cavity wall insulation is appropriate for your house, your house has proper ventilation, the insulation is installed by trained professionals etc. cavity wall insulation is a great option for aiding in increasing the core temperature of your home whilst simultaneously saving a great amount of money on your heating bills in the long-term (thus helping prevent damp occuring in your home) and it’s good for the environment. However, as we’ve just mentioned, it is so important for you to be aware of the materials that live inside your cavity walls. The four core insulation materials that are used in the UK are, mineral wool (rockwool), cavity foam insulation, polystyrene bead insulation and cavity batts.

Common cavity wall Insulation materials

You can find here an overview of each mentioned cavity wall insulation materials, pros (these will include their production, production materials, installation, price per square metre and their thermal conductivity) and their cons.

  • Mineral wool (Rockwool)
  • Cavity Foam Insulation
  • Polystyrene beads
  • Cavity Batts
Side note

The thermal conductivity of cavity wall insulation materials is measured with a λ-value (a lambda value). The better your insulation is, the lower your λ-value will be. This is because the lower your thermal conductivity, how well your insulation can conduct heat energy, the less heat will be lost through your insulation.

Mineral wool

Mineral wool was the first type of insulation to be used in cavity walls, it became popular for our households in the 1950s. Mineral wool is the most commonly used insulation material for residential areas. It is mostly produced from igneous rocks, it is heated and spun into the material you know today as mineral wool. There are many attributes to this form of insulation alternatively there are also some downfalls. Are you interested in finding out? Please see below:-


There are plenty of materials available for the production of mineral wool

Do you remember us saying it is mostly made out of igneous rocks? Aside from its derivation from a naturally occurring substance, it can also be produced out of recycled glass and sand too!

The most environmentally friendly insulation material.

Given its natural origin, and its origin from recycled materials, mineral wool is the easiest insulation material to dispose of because of its recyclability.

Easy to install.

Mineral wool is actually the easiest form of insulation to install. It is easily slid between your inner and outer walls and can be pre-cut to the exact width of the cavity.

Cheap to install.

Costing around £10-15 per square metre (not including labour of course!). The installation of mineral wool definitely won’t hurt your pockets.

Decent insulating performance.

Mineral wool has quite a favourable lambda value of approximately 0.034 W/mk, this means not much of the heat produced in your home will be lost through your mineral wool insulation. This also means you can save a lot of money on heating bills.


Cavity must be clean and spacious.

Prior to the installation your cavity must be inspected, cleared and cleaned for this type of insulation material. Unfortunately the clearing of your cavity wall can be pretty expensive, and must be done by professionals to avoid damage to your property.

Mineral wool isn’t suited to a small cavity space, this means if your home hasn’t got enough room in its cavity walls, the installation of this material will do more damage than good!

Can clump and cause dampness.

Although mineral wool is said to be water resistant, from professional experience here, at First Choice Energy Ltd, mineral wool is not water resistant in the slightest. In many cases of our cavity wall extraction jobs, your houses have been left with chronic dampness inside due to the moist air gathered by the mineral wool insulation.

When mineral wool becomes damp, or even old, it can clump around your brick ties. After many borescope inspections of homes we have surveyed, our professionals have seen much of your mineral wool insulation clumped around the brick ties of your cavity wall! This can seriously damage the structures of your property, an example of the damage it could cause your house is a crack in the rendering of your house.

Fixing any damages caused by the failure of mineral wool insulation can be very expensive.

For more information on this please feel free to read out article of on the cost of damage and cavity wall insulation removal.

Polyurethane foam

Polyurethane foam (PUR) insulation has been available to homeowners since around about 1986. It is used pretty frequently in newer constructions. Polyurethane is essentially a plastic material, it consists of organic units, meaning it is carbon based, joined together to make one long, inert polymer. Thinking of using polyurethane foam as an insulating agent for your home? It is really important for you to be aware of the pros and cons surrounding the use of this material: –


PUR insulation provides an air barrier for your house.

This means there’s less warm air lost from your home. With a lambda value of 0.030 W/mk, polyurethane foam is actually the best insulator of all of the materials, reducing the energy costs of your home

Relatively cheap to install.

Again, not including the cost of labour, polyurethane foam is relatively cheap to install, costing around £20-25 per square metre. Not as cheap as mineral wool, but given its superior insulation performance, it’s still a reasonable price!

PUR will not cause mould in your home

You already know PUR is an inert polymer, this means it is not a food source for mould, even if there is damp in your cavity.


It can cause severe water damage to your home.

Polyurethane foam can shrink over time, this means water can creep into the no longer insulated crevices, and the same goes if the material isn’t installed properly! It is so important to ensure a professional does this for you.

Material reduces in size overtime

A reduction in insulative properties is also a result of the materials shrinking and pulling away from the framing of your cavity walls.

Polyurethane foam expands and fills every corner.

Some may see this as an advantage to the material, however here at First Choice Energy Ltd, we see things a little differently…

If your insulation material fills the entire width of your cavity, then your cavity cannot breathe! It is so important to allow your cavity to breathe otherwise it can gather damp, with no ability to ventilate and attempt to dry out! This will eventually cause dampness in your home.

Polystyrene beads

Expanded polystyrene beads, or EPS, are made of a carbon polymer and are installed into your walls with a bonding agent. The carbon polymers measure around 0.5mm in diameter at the beginning, however, to become the popular shape you know them as today, they must first go through a steaming process. This steaming process then fills them with air, making a larger polystyrene bead of around 3-5mm in diameter. Does this type of insulation catch your fancy? You should know the pros and cons alongside this material-


EPS beads have a durable and lightweight structure.

This makes the little beads easy to install in your home, there’s no large, clumping materials to lug around, and try to manipulate around the structures of your home.

The polystyrene beads are installed with a bonding agent.

The bonding agent sicks the beads together, this means it is easy to install and will leave next to no mess after installation!

Cheap to install.

The lightweight structure, alongside the clean, easy installation makes EUR a cheap option for cavity wall insulation at £10-15 per square metre, again, not including the labour costs of the installer.

Relatively water resistant.

When installed correctly, alongside the bonding agent, EPS insulation beads have a low absorption ability. This means if water, or moisture, does enter the cavity the droplets won’t penetrate or cling to the beads, allowing the material to dry out before causing any damp in your home.

Good insulating performance.

Need we say more? With a λ-value of 0.03-0.034 W/mk, EPS has an insulating performance that ranges between PUR and Mineral wool, saving you money on your energy bills and keeping your home warm!

EPS is recyclable.

One of the ways polystyrene beads are recycled is by being sent to a recycling depot. It is then broken down into its original bead and made into many different other products, such as your coffee cups, or the refrigerator trays in your home.


A clean, spacious cavity is needed for installation.

It sounds pretty trivial, right? Cavities can get very dirty and gritty over time. If you’re having EPS installed, it is so important to ensure the cavity is cleaned prior to the installation, this can be quite costly, depending on the state of the cavity.
If the cavity is not cleaned before EPS is installed, you may be facing the consequences of a failing cavity wall insulation!

Polystyrene beads insulation must be installed properly.

Human error can happen sometimes, if this material is installed incorrectly, i.e., with no/not enough bonding agent, it will cause problems for you!

For example, any home renovations that involve exposing the cavity inside your walls will result in the beads falling out and causing a mess. Without the bonding agent, the beads will also lose some of their water resistant properties, this means dampness in your home is a possibility!

Gaps in your cavity can occur.

The beads can pull away from the crevices of your cavity, or the bonding agent can wear down, this can also cause dampness in your home as the moisture entering your cavity will cling to, and penetrate the internal walls of your home.

If there are gaps in your cavity wall insulation, heat will then escape your home, thus causing you more money on your heating bills.

Cavity batts

Cavity batts have been available for the insulation of your homes for around 30 years, they are used in new builds and extensions in residential areas and also in commercial buildings. This form of cavity wall insulation is made of mineral wool that has been compressed into slabs of varying thicknesses from 50mm to 150mm and they are covered with a water resistant film. Perhaps cavity batts could be the best insulation material for you? Let’s weigh the pros and cons first, shall we?


Cavity batts are lightweight and easy to handle.

The lightweight properties of cavity batts make for an insulation method less likely to clump and hang off your brick ties, reducing any risks of potential expensive damages caused to your home.

Alongside the batts being lightweight, they are easy to handle meaning they’re easier to install into your home too!


One of the cheapest materials to install.

The prices of cavity batts depend on the thickness of the batts you’re going to be installing into your home. Prices for this material range from around £6 per square metre for a batt of 50mm thickness, and will go to about £16 per square metre for a batt of 150mm thickness, potentially saving your purse a good few pounds per square metre of insulation, in comparison to some materials

They are closely fitted to the inner wall of your cavity.

It is now pretty well known, its essential you cavity wall can breathe, especially when insulated. If it can’t breathe, your house is at risk of developing damp problems, and where there’s damp, mould won’t be too far away!

The close fit of the cavity batts to the inner wall of your cavity means there is space between the outer wall of your home and the batts. This allows proper ventilation of your cavity. Meaning, if water does happen to enter the cavity, it is easily dried out, with a very low risk of causing dampness.

They have a water resistant coating.

This works alongside the well-ventilated cavity. Any moisture that happens to gather in the cavity will not be absorbed by the batts due tos water resistant coat on its surface, again reducing the risk of dampness developing in your home dramatically.

Cavity batts have the highest Euroclass Classification (A1) for fire resistance.

This really speaks for itself doesn’t it? A safer way to insulate your home and keep your family warm


Highest lambda value of all the insulation materials.

It’s not necessarily a terrible λ-value, it’s just not the best at 0.037 W/mk. The higher lambda value means that it won’t insulate your home as efficiently as the other materials, perhaps costing you a tiny bit more on your heating bills each year.

Cavity batts can only be installed in the process of building your home.

Because of their structure, it is an unfortunate reality for those of you that may want cavity batts as the insulation material for your ready-built house. To install cavity batts into a house that is already built would mean removing the entire external wall of your home…your home becoming a building site for weeks, and a rather costly renovation, that just isn’t worth it, we’re sure you can agree.


What are the best cavity wall insulation materials for you?

Here at First Choice Energy Ltd, it is our professional opinion that the best insulation materials for you would either be the cavity batts, or the polystyrene beads.

If you are building a home, our recommendation would be to use the cavity batts. Although its insulation performance isn’t as great as the other materials, it’s still pretty good. The pros of cavity batts also outweigh the cons. Their easy installation (if you’re planning on building your home from scratch), cheap installation cost, structure and safety measures are definitely an asset to your home!

Alternatively, if your house has already been built, we cannot recommend this form of insulation. However, we would highly recommend the installation of polystyrene beads into your walls. Although, as we’ve mentioned, human error can cause the failure of your cavity wall insulation, when done properly, EPS is a fantastic choice for your home. Its pros- cheap installation price, mess-free installation, good insulating performance and recyclability, much like the cavity batts, out-weigh the cons of this material.

A quick recap...

Did that help you decide the best type of insulation for your home? Perhaps you would like to know what type of insulation is in your cavity walls? Or are you thinking of cavity wall insulation and are interested in a free survey? Whatever the query, here at First Choice Energy we are happy to answer any question you may have. So why not get in touch?

Request a call back and speak to a proffesional today