EPS Polystyrene Insulation Boards

EPS polystyrene insulation boards for external wall insulation

EPS (expanded polystyrene) insulation boards are the most widely used insulation layer in UK external wall insulation systems. They are lightweight, easy to cut on site, stable in performance and the most cost-effective way to bring a solid wall up to modern U-value targets. At Penguin BM we stock graphite EPS insulation boards in 20-100 mm thicknesses for facades, renders and complete EWI systems - sold per m², with UK delivery or collection from our Amersham store.

What is an EPS insulation board?

An EPS insulation board is a rigid panel made from expanded polystyrene beads fused together under steam. Around 98% of the board is trapped air, which is what gives it its insulating performance. Facade-grade EPS boards are cut to tight tolerances so they can be bonded to the wall, fixed mechanically and covered with a reinforced basecoat and render.EPS for external walls is a different product from the polystyrene used under floors or in lofts. Facade boards are made to be rendered, are dimensionally stable and come in thicknesses suited to EWI. Always check that the board you buy is intended for external wall insulation systems.

Graphite EPS vs white EPS

EPS boards come in two main types. White EPS is the standard board. Graphite EPS (sometimes called grey EPS or graphite polystyrene) contains graphite particles that reflect and absorb radiant heat, lowering the thermal conductivity of the board. In practice this means a thinner graphite board gives the same performance as a thicker white one.

Which EPS thickness do you need?

The thickness you need depends on the existing wall and the U-value you want to reach. For renovation of external walls, a U-value of around 0.30 W/m²K is the usual target in England - check the requirement with your building control body before you order.The table below shows indicative U-values when graphite EPS is added to a typical 225 mm solid brick wall (existing U-value around 2.1 W/m²K).

Indicative values calculated for λ 0.032 W/mK, excluding the effect of fixings and thermal bridges. Your installer or system designer should confirm the U-value for your wall. To reach 0.30 W/m²K on the same wall you would need roughly 90 mm of graphite EPS or around 110 mm of white EPS.

For a detailed explanation, read our external wall insulation thickness guide.

Why use EPS boards for external wall insulation?

• Cost-effective - the lowest price per m² of any EWI insulation board.
• Lightweight - easy to carry up the scaffold and quick to fix, which keeps labour time down.
• Easy to cut and shape - with a hot wire cutter or fine saw, around windows, pipes and corners.
• Stable performance - EPS does not lose insulating value over time.
• Low water absorption - suitable under a reinforced basecoat and render finish.
• Recyclable - EPS offcuts can be recycled.

On attached properties, taller buildings or walls where fire breaks are specified, mineral wool may be required in place of EPS or as fire barriers. Always follow the system specification and Building Regulations for your project.

How EPS boards are installed in an EWI system

1. Prepare the wall - clean, repair and prime where needed. Fit a starter track at the base of the wall.
2. Bond the boards - apply insulation board adhesive using the perimeter-and-dab method and lay the boards in a staggered brick pattern.
3. Fix mechanically - add insulation fixings, typically 6-8 per m². See our EWI fixings guide.
4. Rasp and level - rasp the surface flat and fit corner and window beads.
5. Basecoat and mesh - apply basecoat and embed fibreglass mesh.
6. Prime and render - apply primer and a silicone render or other finish.

All the components you need are in our external wall insulation range.

How much do EPS insulation boards cost?

Our graphite EPS boards are priced per m² and start from £4.16 per m² ex. VAT for 20 mm, rising with thickness up to £13.33 per m² ex. VAT for 100 mm. The boards are only part of the system cost - for full material and installed prices per m², see our guide to external wall insulation cost in the UK.Ordering for several properties or a large project? Trade prices are available on bulk orders - contact our team or call 07515 283453.

Frequently asked questions

What is the difference between EPS and polystyrene insulation board?

There is no difference - EPS stands for expanded polystyrene. "EPS insulation board", "polystyrene insulation board" and "expanded polystyrene insulation board" all describe the same product.

Is graphite EPS better than white EPS?

Graphite EPS has a lower thermal conductivity (around 0.031-0.033 W/mK compared with 0.036-0.040 W/mK for white EPS), so it insulates around 15-20% better at the same thickness. That lets you use thinner boards, which helps where window reveals, sills or roof eaves limit the build-up.

What thickness of EPS do I need for external wall insulation?

For a typical solid brick wall, around 90-100 mm of graphite EPS or 110 mm of white EPS reaches a U-value of about 0.30 W/m²K. Thinner boards (20-30 mm) are used in window reveals and tight details.

Can EPS boards be rendered directly?

No. EPS boards must be covered with a basecoat with embedded fibreglass mesh, then primed and rendered. Render applied directly to EPS will crack.

How do I fix EPS insulation boards to a wall?

EPS facade boards are bonded with insulation board adhesive and then fixed mechanically with insulation fixings, typically 6-8 per m² depending on the wall and exposure.

Can I collect EPS boards in person?

Yes. You can collect your order from our store at 17 White Lion Road, Amersham, HP7 9HZ, or choose UK delivery at checkout.