Independent comparisons. We may earn from shop links. More info

PIR vs EPS insulation boards

Updated: 23 October 2026

You can fit a foil PIR board or a thicker EPS board, and you want the condition rather than a slogan. PIR vs EPS insulation boards is a thickness argument first and a fire-class argument straight after. PIR at about 0.022 W/mK buys the same layer resistance in less depth. It is also the board this comparison does not stock, and on a widely used datasheet it is Euroclass F. The five rows on the [insulation slab comparison](/hub/diy-supplies/insulation-slab) are EPS, a thin XPS sheet, and foam backers. These materials were not hot-box tested. Prices are amazon.co.uk figures from 21 October 2026. A purchase through our links can earn a commission at no extra cost to you.

You can fit a foil PIR board or a thicker EPS board, and you want the condition rather than a slogan. PIR vs EPS insulation boards is a thickness argument first and a fire-class argument straight after.

Our top picks

Triplast Triplast EPS 70 50 mm six-pack

Best overall

Triplast Triplast EPS 70 50 mm six-pack
7.4/10about £47.59
View offer
Triplast Triplast EPS 70 10 mm ten-pack

Alternative

Triplast Triplast EPS 70 10 mm ten-pack
6.4/10about £16.89
View offer
EkoBoard EkoBoard 10 mm XPS underlay

Alternative

EkoBoard EkoBoard 10 mm XPS underlay
6.2/10about £7.99
View offer
On this page
  1. 1.The same resistance needs more EPS
  2. 2.Fire class does not follow the lambda
  3. 3.When EPS is the right board, and when it is not
  4. 4.XPS and wool, in one short aside

The same resistance needs more EPS

Layer resistance is thickness in metres divided by lambda. Fifty millimetres of PIR at 0.022 W/mK is about 2.27 m²K/W. Matching that at 0.038 W/mK, the high end of Triplast’s range, needs about 86 mm of EPS. At 0.030 W/mK it is about 68 mm. That is the layer, not the floor’s U-value. A declared 0.022 W/mK sheet is not in the table. Eurothane GP states that lambda, at least 120 kPa at 10%, and BBA 24/7254. The Triplast six-pack is about £47.59 and prints only Low (0.038–0.030 W/mK).

Fire class does not follow the lambda

Eurothane GP is Euroclass F on the Recticel datasheet, and the foil has to stay dry. A lower lambda is not a better fire class. On 21 October 2026 the live bullet for the 10 mm Triplast pack said EPS is combustible and Euroclass F. That sentence is not on the comparison table. Do not copy it onto the 50 mm pack, the Thermopanel boards, or EkoBoard, and do not move certificate 24/7254 onto Triplast. On a tall external wall, neither foam is the default. Over 11 m the prescriptive route expects A2-s1, d0 or a BS 8414 test assessed to BR 135. Mineral wool is A1 only when its own datasheet says so.
Triplast Triplast EPS 70 50 mm six-pack

Testsieger

Triplast Triplast EPS 70 50 mm six-pack
7.4/10about £47.59
View offer

When EPS is the right board, and when it is not

Choose EPS when you have room for the extra thickness and can accept 0.030–0.038 W/mK. In this set that is the Triplast packs: shared 4.6 from 345, no foil, a messy cut. Neither pack is 86 mm. Choose a declared 0.022 W/mK PIR board when the depth is tight and the fire rules allow Euroclass F. Use that brand’s certificate number. The £47.59 EPS pack does not replace a £144 foil pack if the drawing says 50 mm of PIR. Choose neither foam on a tall external wall. The buying guide sets that stop, and the floor page holds 0.18 W/(m²·K).

XPS and wool, in one short aside

XPS sits beside the pair for load and moisture, typically about 0.033–0.036 W/mK. EkoBoard’s 10 mm board at about £7.99 prints no lambda, so it does not represent that class and does not settle PIR against EPS. Mineral wool is the fire-class aside: A1 only when the datasheet says A1, and usually thicker. Phenolic, about 0.019 W/mK, is not stocked here.

Common questions

When is 0.022 W/mK worth paying for?
When the build-up has no room for the extra EPS thickness and the fire rules allow a Euroclass F foam. Fifty millimetres at 0.022 W/mK is about 2.27 m²K/W of layer resistance. Matching that with EPS at 0.038 W/mK takes about 86 mm, and at 0.030 W/mK about 68 mm. If you have that depth, the lower lambda is a cost, not a requirement. The layer resistance is still not the floor’s U-value.
How much thicker does EPS need to be for the same resistance?
About 86 mm of EPS at 0.038 W/mK to match 50 mm of PIR at 0.022 W/mK, because 2.27 × 0.038 is about 0.086 m. At 0.030 W/mK, the low end of the range Triplast prints, the same sum is about 68 mm. Treat both as rounded layer arithmetic, not as a specification for your floor. Triplast does not declare a single lambda inside that range.
Is PIR better in a fire because it insulates better?
No. Eurothane GP is Euroclass F on Recticel’s datasheet at the same time as it declares 0.022 W/mK. A lower lambda does not change that class. The live caution on one Triplast EPS listing also says combustible and Euroclass F, and that sentence stays on that listing. Tall external walls look for A2-s1, d0 or a tested system, not for the better insulator.
Why is there no PIR board in this comparison?
Because the five kept amazon.co.uk rows are small-format EPS, a 10 mm XPS underlay, and two foam tile backers. Full-size 2400 × 1200 mm foil PIR appeared in search on 21 October 2026 from about £144 for four sheets to £419.99 for twelve, and those packs are not rows here. The £47.59 Triplast six-pack is not one of them.
Does EPS 70 beat PIR on strength?
Not on the evidence in these listings. EPS 70 is a compressive class name. The British Plastics Federation’s typical table puts that class at 70 kPa at 10% compression, and Triplast does not print a kilopascal figure, so you should not assign 70 kPa to the packs. Eurothane GP states at least 120 kPa at 10% on its own sheet. Different products, different declared numbers.
Can I use either board on a high external wall?
No, not as the default. Over 11 m, the prescriptive route expects A2-s1, d0 or better, or a BS 8414 / BR 135 route, and an 18 m ban covers specified new residential buildings. PIR at Euroclass F and EPS with a combustible caution both fail that default. Use a product whose own datasheet states the class the wall requires, such as a mineral wool that declares A1.
Is the Triplast BBA line the same certificate as Eurothane’s 24/7254?
No. Eurothane GP cites BBA 24/7254 on the Recticel datasheet. Triplast’s bullet says BBA certified for BS EN 13163:2012 and the capture has no certificate number. Those are different products. Do not move 24/7254, the 120 kPa figure, or the single lambda of 0.022 onto the EPS packs.

Related pages

Best insulation boards

Insulation slab

Insulation board buying guide: nation, then lambda

Insulation boards for floors: why 10 mm is not 0.18

How to fit insulation boards and when you should stop

Sources

Public UK sources and the amazon.co.uk listings compared on this page. Prices are the amazon.co.uk figures stored on 21 October 2026. Updated 22.10.2026.

  1. Approved Document L 2026, GOV.UK (retrieved 22.10.2026)
  2. Scottish building standards handbook 2022, section 6.2 (retrieved 22.10.2026)
  3. Ban on combustible materials, GOV.UK (retrieved 22.10.2026)
  4. Circular letter 02/2022, combustible materials (retrieved 22.10.2026)
  5. Recticel Eurothane GP datasheet (retrieved 22.10.2026)
  6. Polyfoam XPS: ground floor insulation (retrieved 22.10.2026)
  7. IMA: PIR floor insulation guidelines, November 2024 (retrieved 22.10.2026)
  8. HSE cellular plastics, HSG92 (retrieved 22.10.2026)