Insulation board buying guide
Updated: 23 October 2026
You have a listing open that says insulation board, and the star rating is the loudest number on the page. An insulation board buying guide starts with the part of the building you are covering, and with the UK nation that building sits in. A shed wall, a ground floor in England, and the outside wall of a block of flats do not take the same slab. Lambda, thickness, grade, facing, and fire class come before the price. The five small boards stay on the [insulation slab comparison](/hub/diy-supplies/insulation-slab). These boards were not tested in a lab. A purchase through our links can earn a commission at no extra cost to you.
You have a listing open that says insulation board, and the star rating is the loudest number on the page.
You have a listing open that says insulation board, and the star rating is the loudest number on the page. An insulation board buying guide starts with the part of the building you are covering, and with the UK nation that building sits in. A shed wall, a ground floor in England, and the outside wall of a block of flats do not take the same slab. Lambda, thickness, grade, facing, and fire class come before the price. The five small boards stay on the insulation slab comparison. These boards were not tested in a lab. A purchase through our links can earn a commission at no extra cost to you.
Our top picks
| Badge | Product | Material | Thickness | Lambda | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  Triplast Triplast EPS 70 50 mm six-pack | EPS 70 | 50 mm | 0.030–0.038 W/mK | 7.4 | about £47.59 | View offer |
| Best value |  Thermopanel Thermopanel 15 mm tile backer | Foam | 15 mm | 0.027 W/mK | 7.2 | about £15.99 | View offer |
| Alternative |  EkoBoard EkoBoard 10 mm XPS underlay | XPS | 10 mm | n/a | 6.2 | about £7.99 | View offer |
On this page
Name the element and the nation first
Start by naming the element. A timber shed lining, a new ground floor, and the external wall of a relevant residential building are three different jobs. The five boards here are small-format EPS, a 10 mm XPS underlay, and two foam tile backers. None is a 2400 × 1200 mm foil-faced PIR sheet.
England’s Approved Document L 2026 prints 0.16 W/(m²·K) for a new-dwelling roof, 0.26 for a wall, 0.18 for a floor, and 0.20 for a party wall. In existing dwellings a new wall and a new floor are both 0.18. Those changes take effect on 24 March 2027. Scotland’s Table 6.3 prints 0.22, 0.18, and 0.15 for wall, floor, and roof. Showing an extension floor against 0.18 is a calculation, which starts on the floor guide.
Read lambda and thickness together
Lambda is thermal conductivity, in watts per metre-kelvin. Branded PIR is often about 0.022 W/mK, EPS about 0.030–0.038, and XPS about 0.033–0.036. The Triplast rows only print a range, Low (0.038–0.030 W/mK), which is not one declared lambda.
Resistance of a layer is thickness in metres divided by lambda. Fifty millimetres at 0.022 W/mK is about 2.27 m²K/W. Fifty millimetres at 0.038 W/mK is about 1.32 m²K/W. Neither figure is the U-value of the finished floor, wall, or roof. EkoBoard’s 10 mm XPS listing has no lambda, so you cannot run the division. Thermopanel prints 0.027 W/mK on a backer whose material field only says Foam.
Grade, facing, and what the box contains
EPS 70 is a compressive class, not a 70 mm sheet. On the British Plastics Federation’s typical table it means 70 kPa at 10% compression. Triplast’s listing prints no kilopascal figure, so do not assign 70 kPa to these packs.
The Triplast packs are square-edged white EPS with no foil, adhesive, or fixings. Thermopanel’s box is one board: no washers, screws, tape, adhesive, or heating mat, even though the bullet talks about wet areas and electric underfloor heating. EkoBoard is one 10 mm XPS sheet with no British Standard number. A BBA line for BS EN 13163:2012 has no certificate number in the capture.
Fire class before a tall wall
Foam is the wrong default on the external wall of a tall residential building. Specified new residential buildings with a storey at least 18 m above ground are covered by the combustible-materials ban. Over 11 m, Approved Document B’s prescriptive route expects A2-s1, d0 or better, or a BS 8414 test assessed under BR 135.
None of the five listings prints a Euroclass. 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, so do not copy it onto the other four. If the wall might sit over 11 m, stop. Which of the five fits a small job is on best insulation boards.
Common questions
What should I decide before I look at a price?
Decide the element and the nation, then whether you have a declared lambda and a thickness you can actually fit. A shed lining, a ground floor, and an external wall over 11 m are three different jobs, and England, Scotland, Wales, and Northern Ireland do not share one wall figure. The price on amazon.co.uk is the last check, after the board can legally and physically sit in that place.
What is a lambda, and why do I need the thickness as well?
Lambda is how readily the material conducts heat, in W/mK. The resistance of a layer is thickness in metres divided by that number. Fifty millimetres at 0.022 W/mK is about 2.27 m²K/W, and 50 mm at 0.038 W/mK is about 1.32 m²K/W. Those are layer resistances. They are not the U-value of the finished floor or wall.
Does EPS 70 mean the sheet is 70 mm thick?
No. EPS 70 is a compressive class. On the British Plastics Federation’s typical table it means 70 kPa at 10% compression. Triplast’s listing does not print a kilopascal figure, so you should not copy 70 kPa onto those packs. Read the millimetre thickness in the title separately: 50 mm or 10 mm on the two Triplast rows.
Can I use these foam boards on a tall block of flats?
Not as the default on the external wall. Specified new residential buildings are covered by the 18 m combustible-materials ban, and over 11 m the prescriptive route in Approved Document B expects A2-s1, d0 or better, or a BS 8414 / BR 135 route. None of these five listings prints that class. A masonry-cavity exception is not permission to clad a high wall with these boards.
Is a BBA line on the title the same as a certificate number?
No. Triplast’s bullet says BBA certified for BS EN 13163:2012, and the capture has no certificate number. Eurothane GP’s datasheet cites BBA 24/7254, and that number belongs to that PIR board, not to these EPS packs. Treat a title line without a number as a claim you have not checked.
Why do two Triplast packs share one star rating?
Both the 50 mm six-pack and the 10 mm ten-pack show 4.6 from 345 on amazon.co.uk, and the United Kingdom review text matches. The same pattern sits on the two Thermopanel boards at 4.5 from 349. A review that mentions 6 mm or 7 mm is in that shared block. It is not a measurement of every thickness the title names.
Related pages
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.
- Approved Document L 2026, GOV.UK (retrieved 22.10.2026)
- Scottish building standards handbook 2022, section 6.2 (retrieved 22.10.2026)
- Ban on combustible materials, GOV.UK (retrieved 22.10.2026)
- Circular letter 02/2022, combustible materials (retrieved 22.10.2026)
- Recticel Eurothane GP datasheet (retrieved 22.10.2026)
- Polyfoam XPS: ground floor insulation (retrieved 22.10.2026)
- IMA: PIR floor insulation guidelines, November 2024 (retrieved 22.10.2026)
- HSE cellular plastics, HSG92 (retrieved 22.10.2026)