When comparing PIR (polyisocyanurate) vs EPS (expanded polystyrene) insulated plasterboard, the difference comes down to performance versus thickness. PIR gives you stronger insulation in a thinner board, while EPS is cheaper but needs more depth to achieve the same result.
That might sound like a small distinction, but once you start planning a real project, it quickly becomes the deciding factor. Room size, wall type, and compliance targets all come into play.
Here’s the short version:
- PIR performs better per millimetre and keeps the wall build-up slimmer
- EPS costs less upfront but increases overall thickness
- The right option depends on your space, your target U-value, and how much depth you can realistically use
How Each Board Is Made and Fixed
Both PIR and EPS insulated plasterboard follow the same basic principle, so from an installation point of view, they feel very familiar.
Same system, different insulation core
Each board combines a rigid insulation layer bonded to a 12.5mm plasterboard face. That means you are insulating and finishing the wall in a single step, which keeps things efficient on site.
They are usually fixed to masonry walls using dot-and-dab adhesive, though mechanical fixings can also be used where needed. The process is straightforward, which is one of the reasons these systems are so widely used in internal wall insulation projects. Online Insulation Sales stocks both PIR and EPS boards for UK retrofit, with U-value data listed against each product so you can confirm the specification before ordering.
Thermal Performance Between PIR vs EPS
Thermal performance is where the real difference between these two materials becomes clear. It is also the reason most people end up choosing one over the other.
Why conductivity matters
PIR has a thermal conductivity of around 0.022 to 0.023 W/mK, while EPS typically falls between 0.032 and 0.038 W/mK. Lower values mean better insulation, so PIR simply does more work with less material.
Here’s what that means in practice. To hit a specific U-value, PIR does not need to be as thick as EPS. And when you are working internally, that difference matters.
Real-world U-value comparison
On a standard 215mm solid brick wall, the gap between the two becomes more tangible.
PIR-backed boards can reach around 0.30 W/m²K with roughly 80mm of insulation. EPS, on the other hand, usually needs 100mm or more to reach the same level.
| PIR | EPS | |
| Thermal conductivity | 0.022–0.023 W/mK | 0.032–0.038 W/mK |
| 50mm U-value (solid brick) | ~0.50 W/m²K | ~0.60–0.65 W/m²K |
| Depth for 0.30 W/m²K | 70–80mm | 100mm+ |
| Material cost | Higher | Lower |
| Best use case | Tight spaces, strict targets | Budget-led projects |
So while both materials can meet the same targets, PIR gets you there with less thickness, which is often the deciding factor.
Floor Space Lost: Why Thickness Matters
Once you move from theory into a real room, thickness stops being just a number on a spec sheet.
Small differences add up quickly
A PIR board designed to hit 0.30 W/m²K usually ends up around 92.5mm thick in total. An EPS board achieving the same result will often push past 112mm.
That difference might not sound dramatic at first. But when you apply it across multiple walls, you start to feel it. Window reveals become tighter, furniture placement becomes more restricted, and the room can feel noticeably smaller.
In older UK homes, where space is already limited, this is often the point where PIR becomes the more practical option.
Where Each Board Has the Advantage
Both materials have their place, and the right choice depends on what the project is trying to achieve.
When EPS is a good fit
EPS tends to work well in situations where thermal targets are not especially demanding and there is enough space to accommodate extra thickness.
You will often see it used in loft rooms, newer properties, or secondary spaces like garages and utility rooms. In these cases, saving on material cost can make sense because the impact of added depth is minimal.
When PIR is the better option
PIR is usually the safer and more reliable choice for solid brick walls, particularly in older properties where meeting Part L targets is a priority.
Because it achieves those targets with less thickness, it helps you stay compliant without compromising too much on room size. That balance is why PIR is so commonly specified for internal wall insulation.
Material Cost Between PIR vs EPS
Cost is always part of the decision, and at first glance, EPS has the advantage.
Looking beyond the board price
PIR insulated plasterboard typically costs more per square metre than EPS. However, focusing only on that figure can be misleading.
EPS requires more thickness to achieve the same performance, which can increase installation materials and reduce usable space. When you factor those elements in, the gap between the two options often narrows.
In many projects, the thinner profile of PIR ends up justifying the higher upfront cost, especially where space is limited.
Confirming the Right Specification Before Ordering
Before choosing between PIR and EPS insulated plasterboard, it is worth taking a step back and confirming the numbers properly.
Get the calculation right first
A U-value calculation will tell you exactly what insulation thickness is required for your wall. To do this accurately, you need to know the wall construction, the target U-value, and how much internal space you can afford to lose.
Once those details are clear, the choice between PIR and EPS becomes much easier to justify.
For most solid brick retrofit projects with limited space, PIR remains the standard specification. If your project has more flexibility or lower thermal requirements, EPS can still be a viable option.
You can compare and buy insulated plasterboard from Online Insulation Sales, where both PIR and EPS systems are available in a range of thicknesses to suit different specifications.
Choose the Right Board and Order with Confidence
Choosing between PIR and EPS insulated plasterboard is really about balancing performance, cost, and space. There is no one-size-fits-all answer, but in most internal wall retrofits, PIR tends to come out ahead because it delivers strong performance without taking up as much room.
The next step is to confirm your U-value, check your available depth, and order the correct board with a sensible allowance for waste. Once that is in place, the installation itself is relatively straightforward.
FAQs
What is the difference between PIR and EPS insulated plasterboard?
PIR provides better thermal performance per millimetre, while EPS is more cost-effective but requires greater thickness to achieve the same result.
Which insulated plasterboard is better for solid brick walls?
PIR insulated plasterboard is typically better for solid brick walls because it meets thermal targets with less thickness, which helps preserve internal space.
How thick does insulated plasterboard need to be to meet Part L?
For solid brick walls, around 70 to 80mm of PIR insulation is usually enough to reach 0.30 W/m²K. EPS generally requires 100mm or more.
Can both PIR and EPS insulated plasterboard be fixed using dot and dab?
Yes, both types can be installed using dot-and-dab adhesive or mechanical fixings, depending on the wall condition and board specification.
Where can I buy PIR and EPS insulated plasterboard?
Online Insulation Sales stocks PIR and EPS insulated plasterboard across a range of thicknesses and includes U-value performance data for each system, which helps with specification before ordering.