Guide

Bonded bead insulation

The usual way to fill a cavity wall in Ireland. What goes in the wall, how it's done in a day, and what it costs.

Figures checked against seai.ie on 28 October 2026. How we check

Bonded bead is the usual way cavity walls are insulated in Ireland. Small polystyrene beads are coated with a glue as they're blown into the cavity through holes drilled in the outer wall. The glue sets and holds the beads together.

It usually takes a day for a house. Pumped bonded bead costs about €7.50 to €13 per m² including VAT, according to one Irish cost guide.

What bonded bead is

The beads are expanded polystyrene (EPS), the same kind of material as polystyrene packaging, made in small round beads. Some products use grey beads with graphite added, which insulate a little better. As the beads go into the wall, a binder is sprayed onto them so they stick together into one solid fill.

Because they're bonded, the beads don't pour out if you drill into the wall later to hang a shelf or run a cable. That's the main reason bonded bead is used instead of loose beads.

How the job is done

Survey.The installer checks every wall, drills a test hole and looks into the cavity with a camera. They check the cavity width and look for rubble or old insulation.
Vents and flues.Air vents through the wall are sleeved, so the bead doesn't block them. Flues are checked.
Drilling.A pattern of small holes is drilled through the mortar joints or render of the outer wall.
Filling.The bead and binder are pumped in, hole by hole, from the bottom of the wall up, until the cavity is full.
Making good.The holes are filled with mortar or render to match the wall as closely as possible.
Paperwork.The installer gives you what SEAI needs for the grant.

One Dublin insulation company says it's usually installed in a single day (Osber).

Bonded bead, fibre and foam compared

	Bonded bead	Blown mineral fibre	Foam
What it is	Polystyrene beads with a binder	Loose glass or rock wool fibre	Foam injected into the cavity
Spills out if drilled later	No, the beads are bonded	Can, a little	No
Fills narrow or uneven cavities	Flows well	Well	Depends on the product
What to ask	The product's certificate	The product's certificate	The product's certificate

Whatever product is used, SEAI's guide says to ask whether it will reach a U-value of at least 0.27 W/m²K, which the grant needs (SEAI guide). It also says cavity wall installers must be registered with NSAI.

What it costs

€7.50 to €13 per m² for pumped bonded bead, incl. materials, labour and VAT (ShamFix, 31 July 2026).
€1,500 median for a semi-D and €2,250 for a detached house, incl. VAT (SEAI median installed costs, H1 2025, incl. VAT, as published by saveonheat.ie (updated 13 October 2026)).
About €200 for a semi-D after the €1,300 SEAI grant.

Questions to ask before you agree

Which product will you use, and is it certified for cavity walls?
Will it reach a U-value of 0.27 W/m²K?
Have you checked the cavity with a camera, on every wall?
How will you match the filled holes to my wall?
What happens to my air vents?
Is VAT in the price?

Questions people ask

What is bonded bead insulation?

Small expanded polystyrene beads coated with a binder as they're blown into a cavity wall. The binder sets and holds the beads together, so they don't pour out if the wall is drilled later.

How much does bonded bead cost?

About €7.50 to €13 per m² including VAT, according to one Irish cost guide. SEAI's median installed cost for cavity insulation in a semi-D was €1,500 in H1 2025, or about €200 after the grant.

Can I drill into a wall with bonded bead?

Yes. That's the point of the binder: the beads are stuck together, so they stay in the wall.

Will the holes show?

They're filled with mortar or render to match the wall. On brick or coloured render they can show slightly, so ask how the installer will match them.

How long does it take?

Usually one day for a house. The contractor drills a pattern of small holes in the outer wall, pumps the insulation in and fills the holes to match.

Keep reading

Cavity wall insulation costCosts by house type, before and after the grant.Read more Is my house suitable?Check your walls first.Read more Cavity wall insulation and dampWhen to be careful.Read more

Sources (3)

Prices and facts on this page were checked against these published pages. We are not connected to these businesses.

Osber: osber.ie
ShamFix: shamfix.ie
saveonheat.ie: saveonheat.ie

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