Table of Contents

Bonded Bead Insulation Explained

Written by: Briain Kelly

Published: February 10, 2026

Last updated: February 10, 2026

Reading time: 4 mins

Bonded bead insulation is a very popular choice for retrofitting homes due to its easy application and effectiveness in making your home more comfortable and energy efficient.

Our guide explains how bonded bead insulation works and where it is used. We also explain its pros and cons compared to other insulation forms, and whether it is the best choice for your home.

What is bonded bead insulation?

Bonded bead insulation is the name given for cavity wall insulation made from polystyrene beads. The insulation consists of two elements:

  • Polystyrene Beads: Grey beads of Expanded Polystyrene (EPS) that are roughly 2mm – 9mm in diameter.

  • Bonding Agent: An adhesive bonding agent that allows the beads to form a solid mass after they have been injected into the wall.

How does bonded bead insulation work?

The process for using bonded bead insulation is actually very simple, with installers using specialised equipment to fill a cavity wall in a matter of hours:

  • 1
    The installer drills holes in the mortar joints of the external wall.
  • 2
    A specialised hopper is used to pump the EPS beads into the cavity.
  • 3
    An adhesive is mixed with the EPS beads during injection.
  • 4
    The small beads flow like a thick liquid to fill up the cavity space.
  • 5
    The process is repeated along the wall until the cavity is full.
  • 6
    The adhesive sets, forming a solid layer of insulation.

Once the beads harden, they form an evenly distributed layer of insulation the width of the cavity space, which is water repellent and resistant to decay.

Applications of Bonded Bead Insulation

The main use of polystyrene bead insulation is in retrofitting older homes with cavity wall insulation. There are a number of technical and practical reasons why EPS beads are becoming popular for cavity insulation.

  • Small size: Each bead is very small on its own. This means that a steady flow can be pumped through a very small gap. This leads to our second point.

  • Minimal Construction: With bonded beads there is very little work that actually needs to be done on the fabric of the building. Certainly less than with internal or external insulation.

Outside of cavity wall insulation, bonded beads are also used in construction to fill awkward void spaces due to their free-flowing nature.

Cost of Bonded Bead Insulation

The average semi-detached home in Ireland will pay approximately €1,500 for cavity wall insulation. This is a median price, and your costs will be affected by factors that affect how much insulation is needed.

  • Cavity Thickness: A cavity wall could be anywhere from 50mm to 150mm thick.

  • Wall Height: The height of the walls in your home.

You might expect to pay between €35 and €50 per square metre for bonded bead insulation. This includes both the material and installation costs. Prices vary by region and installer.

Grants for Bonded Bead Insulation

There are no specific grants for bonded bead insulation, but this is one of the materials that you are most likely to be using if applying for a cavity wall grant. The SEAI offers grants of between €700 and €1,800 for cavity wall insulation, with the value of the grant depending on your property type.

Read more about Home Insulation Grants.

Benefits of Cavity Bead Insulation

Bonded Bead is relatively simple to install in homes, it just has to be pumped into the cavity wall from outside through a hole drilled into the wall.

Because the installation work takes place outside your home, there is no disruption to life going on inside during the works.

Bonded bead insulation is materially inexpensive, consisting solely of EPS beads and the bonding agent. This is especially true compared to expanding foam.

Unlike materials such as blown wool, EPS beads won’t shift or settle over time as long as they have been installed correctly with the right amount of binder. This ensures that you retain complete coverage of the cavity space.

Cavity insulation is the most cost effective way to insulate a wall. It is a fraction of the price of internal or external insulation, with a grant available that can cover up to 80% of the cost. Cavity insulation is also the easiest way to make your home heat pump ready. 

Potential Drawbacks of Bonded Bead Insulation

Before installation, cavity walls must be checked for existing damp issues, damaged wall ties, or debris in the cavity. If your cavity wall already has damp problems that have not been visible or addressed, then cavity insulation can make it worse by acting as a moisture bridge.

If the insulation is not properly installed and there are gaps in its coverage of the cavity, these gaps can act as cold bridges allowing heat to escape.

Bonded Bead vs Other Cavity Wall Insulation

Polystyrene beads are not the only type of insulation which can be used for cavity spaces, but these are dependent on when you are insulating the space.

When it comes to home retrofits, the best option is to pump insulation into the cavity space from outside. Anything else will require dismantling the wall, something that will make your home improvements much more disruptive, time consuming, and expensive.

Retrofitting Cavity Insulation

Aside from bonded beads there are only really two other methods of pumping insulation into a cavity space are spray foam and blown fibre insulations.

Spray foam gives an excellent thermal performance, but is considerably more expensive than bonded bead insulation. Insurers and lenders may also be wary of any home with spray foam installed.

Blown fibre insulation consists of either cellulose or mineral wool insulation in loose form. This is then blown into the cavity space from outside using air pressure. Cellulose is generally not recommended for cavity walls as it can absorb water.

Blown mineral wool is an option; but the loose nature of the fibres means that you may have an issue with it settling over time and leaving air gaps.

Cavity Insulation in New Builds

In newly built homes, insulation is added to the cavity space during construction. Since this is being done as the walls are going up, builders have more options than pumped or blown-in insulation.

During the construction phase of new homes, it is more common to use slabs of mineral wool or solid poly boards of insulation for cavity walls.

Frequently Asked Questions

Bonded bead insulation should last for the entire lifetime of your property if properly installed. At the very least the system should have an expected lifespan of 25 years.

While it has some other specialised applications, bonded bead EPS insulation is mostly used for cavity walls.

Bonded bead insulation can be installed in just a few hours, depending on the size of your home.

No, historic buildings need extra care with moisture management when it comes to installing insulation. While most historic buildings are more likely to have solid walls, where they do have cavity walls, a natural, breathable fibre is preferred.

If you have installed bonded bead insulation in a semi-detached or terraced house, you will need to install cavity barriers to stop the beads from flowing over the property line on exterior walls. If you have a cavity party wall you want to insulate, this may need approval from your neighbour.

Author:

Briain Kelly
EDITOR

Briain Kelly is a Leinster based journalist and content creator who has been writing about energy efficiency and renewable energy technologies for several years now. He researches the latest news in multiple areas related to solar power, electric vehicles, heat pumps, and home energy upgrades. His writing includes both technological developments and government policy.

Bonded Bead Insulation Explained

Published: February 10, 2026

Last updated: February 10, 2026

Written by: Briain Kelly

Reading time: 4mins

Bonded bead insulation is a very popular choice for retrofitting homes due to its easy application and effectiveness in making your home more comfortable and energy efficient.

Our guide explains how bonded bead insulation works and where it is used. We also explain its pros and cons compared to other insulation forms, and whether it is the best choice for your home.

What is bonded bead insulation?

Bonded bead insulation is the name given for cavity wall insulation made from polystyrene beads. The insulation consists of two elements:

  • Polystyrene Beads: Grey beads of Expanded Polystyrene (EPS) that are roughly 2mm – 9mm in diameter.

  • Bonding Agent: An adhesive bonding agent that allows the beads to form a solid mass after they have been injected into the wall.

How does bonded bead insulation work?

The process for using bonded bead insulation is actually very simple, with installers using specialised equipment to fill a cavity wall in a matter of hours:

  • 1
    The installer drills holes in the mortar joints of the external wall.
  • 2
    A specialised hopper is used to pump the EPS beads into the cavity.
  • 3
    An adhesive is mixed with the EPS beads during injection.
  • 4
    The small beads flow like a thick liquid to fill up the cavity space.
  • 5
    The process is repeated along the wall until the cavity is full.
  • 6
    The adhesive sets, forming a solid layer of insulation.

Once the beads harden, they form an evenly distributed layer of insulation the width of the cavity space, which is water repellent and resistant to decay.

Applications of Bonded Bead Insulation

The main use of polystyrene bead insulation is in retrofitting older homes with cavity wall insulation. There are a number of technical and practical reasons why EPS beads are becoming popular for cavity insulation.

  • Small size: Each bead is very small on its own. This means that a steady flow can be pumped through a very small gap. This leads to our second point.

  • Minimal Construction: With bonded beads there is very little work that actually needs to be done on the fabric of the building. Certainly less than with internal or external insulation.

Outside of cavity wall insulation, bonded beads are also used in construction to fill awkward void spaces due to their free-flowing nature.

Cost of Bonded Bead Insulation

The average semi-detached home in Ireland will pay approximately €1,500 for cavity wall insulation. This is a median price, and your costs will be affected by factors that affect how much insulation is needed.

  • Cavity Thickness: A cavity wall could be anywhere from 50mm to 150mm thick.

  • Wall Height: The height of the walls in your home.

You might expect to pay between €35 and €50 per square metre for bonded bead insulation. This includes both the material and installation costs. Prices vary by region and installer.

Grants for Bonded Bead Insulation

There are no specific grants for bonded bead insulation, but this is one of the materials that you are most likely to be using if applying for a cavity wall grant. The SEAI offers grants of between €700 and €1,800 for cavity wall insulation, with the value of the grant depending on your property type.

Read more about Home Insulation Grants.

Benefits of Cavity Bead Insulation

Bonded Bead is relatively simple to install in homes, it just has to be pumped into the cavity wall from outside through a hole drilled into the wall.

Because the installation work takes place outside your home, there is no disruption to life going on inside during the works.

Bonded bead insulation is materially inexpensive, consisting solely of EPS beads and the bonding agent. This is especially true compared to expanding foam.

Unlike materials such as blown wool, EPS beads won’t shift or settle over time as long as they have been installed correctly with the right amount of binder. This ensures that you retain complete coverage of the cavity space.

Cavity insulation is the most cost effective way to insulate a wall. It is a fraction of the price of internal or external insulation, with a grant available that can cover up to 80% of the cost. Cavity insulation is also the easiest way to make your home heat pump ready. 

Potential Drawbacks of Bonded Bead Insulation

Before installation, cavity walls must be checked for existing damp issues, damaged wall ties, or debris in the cavity. If your cavity wall already has damp problems that have not been visible or addressed, then cavity insulation can make it worse by acting as a moisture bridge.

If the insulation is not properly installed and there are gaps in its coverage of the cavity, these gaps can act as cold bridges allowing heat to escape.

Bonded Bead vs Other Cavity Wall Insulation

Polystyrene beads are not the only type of insulation which can be used for cavity spaces, but these are dependent on when you are insulating the space.

When it comes to home retrofits, the best option is to pump insulation into the cavity space from outside. Anything else will require dismantling the wall, something that will make your home improvements much more disruptive, time consuming, and expensive.

Retrofitting Cavity Insulation

Aside from bonded beads there are only really two other methods of pumping insulation into a cavity space are spray foam and blown fibre insulations.

Spray foam gives an excellent thermal performance, but is considerably more expensive than bonded bead insulation. Insurers and lenders may also be wary of any home with spray foam installed.

Blown fibre insulation consists of either cellulose or mineral wool insulation in loose form. This is then blown into the cavity space from outside using air pressure. Cellulose is generally not recommended for cavity walls as it can absorb water.

Blown mineral wool is an option; but the loose nature of the fibres means that you may have an issue with it settling over time and leaving air gaps.

Cavity Insulation in New Builds

In newly built homes, insulation is added to the cavity space during construction. Since this is being done as the walls are going up, builders have more options than pumped or blown-in insulation.

During the construction phase of new homes, it is more common to use slabs of mineral wool or solid poly boards of insulation for cavity walls.

Frequently Asked Questions

Bonded bead insulation should last for the entire lifetime of your property if properly installed. At the very least the system should have an expected lifespan of 25 years.

While it has some other specialised applications, bonded bead EPS insulation is mostly used for cavity walls.

Bonded bead insulation can be installed in just a few hours, depending on the size of your home.

No, historic buildings need extra care with moisture management when it comes to installing insulation. While most historic buildings are more likely to have solid walls, where they do have cavity walls, a natural, breathable fibre is preferred.

If you have installed bonded bead insulation in a semi-detached or terraced house, you will need to install cavity barriers to stop the beads from flowing over the property line on exterior walls. If you have a cavity party wall you want to insulate, this may need approval from your neighbour.

Author:

Briain Kelly
EDITOR

Briain Kelly is a Leinster based journalist and content creator who has been writing about energy efficiency and renewable energy technologies for several years now. He researches the latest news in multiple areas related to solar power, electric vehicles, heat pumps, and home energy upgrades. His writing includes both technological developments and government policy.

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