The best insulation slabs, compared.
Top pick: Triplast EPS 70 50 mm six-pack – Highest score at 74: the only 50 mm wall-and-floor sheet, 4.6 from 345 reviews, at about £47.59. The lambda stays a range. Best value: Thermopanel 15 mm tile backer – About £15.99 with a stated 0.027 W/mK and 4.5 from 349 reviews. The 40 mm board prints the same lambda at about £20.89. Updated 22.10.2026.
An insulation slab is a rigid board for a floor, a wall, a roof or a wet room in the UK. Rolls, mats, blankets and edge tape are not this product. You match the board to the element: thickness, a declared lambda, a compressive grade, and a fire class. EPS 70 is a compressive class, not a thickness. A lambda shown only as a range is not one declared figure. Layer resistance is thickness in metres divided by lambda, and it is not the U-value of the finished floor. England’s Approved Document L (2026) limits whole-element U-values, including 0.18 W/(m²·K) for floors. Scotland’s Table 6.3 uses 0.22 for walls and 0.18 for floors. Above 11 m, the English prescriptive route expects A2-s1, d0 or better, so foam is the wrong default on a tall residential wall. Foam floor boards go above the damp-proof membrane. How a lower lambda changes the depth you need is set out in [PIR and EPS slabs](/hub/diy-supplies/insulation-slab/sub/insulation-slab-pir-vs-eps).
An insulation slab is a rigid board for a floor, a wall, a roof or a wet room in the UK. Rolls, mats, blankets and edge tape are not this product.
18 products checked · 58 hrs invested · +21,400 readers
Swipe for more
1-2 of 5
Personal buying guide
Question 1 of 2
What are you insulating?
Six square-edged EPS 70 sheets, each 1200 × 600 × 50 mm, make up this pack at £47.59. Across 345 amazon.co.uk reviews the line is 4.6, and the first 50 United Kingdom bodies match the 10 mm pack, so a note about sheets measuring about 7 mm is not a measurement of these 50 mm boards. Reviewers who lined a summerhouse, shed or workshop roof call the sheets light and easy to cut, and they also say the cut throws beads and that the board feels fragile next to denser foam. The bullet prints lambda as a range, 0.030–0.038 W/mK, rather than one declared figure, and the coverage field prints 7.75 square feet while six sheets at the stated size are 4.32 m². The BBA wording for BS EN 13163:2012 has no certificate number on the listing, and no fire class is printed. Fixings are not in the box; reviewers stick or place the sheets themselves. It is the top pick in this set when you want the only 50 mm wall-and-floor sheet, and the wrong board when the floor has to meet a U-value or the wall is a tall residential elevation.
Pros
Cons
Best for: You are lining a small outbuilding and 50 mm of EPS is the depth you can fit.
Less suitable: A floor that must meet 0.18 W/(m²·K), a tall external wall, or a job that needs one declared lambda.
Specifications
Common questions
Is the lambda a single declared figure?
No. The bullet prints Low (0.038–0.030 W/mK). That is a range, not one declared lambda for this pack.
Does the box include fixings?
No. The listing does not include fixings, adhesive or a foil facing. Reviewers describe placing or sticking the sheets themselves.
Do the 4.6 stars measure only these 50 mm sheets?
The star line is 4.6 from 345, and the United Kingdom review text matches the 10 mm pack. A review that measured about 7 mm is not a measurement of this 50 mm pack.
Ten white EPS 70 sheets, each 600 × 400 × 10 mm, come to £16.89, and the pack is listed at 420 g. The lambda is the same printed range as the 50 mm pack, 0.030–0.038 W/mK, and the star line is the same 4.6 from 345. The listing also sells the sheets for packaging and craft, and the shared review block mixes summerhouse lining with model-making. One reviewer wrote that sheets were about 7 mm rather than 10 mm; the listing does not say which pack that person bought. The coverage field prints 2.58 square feet, while ten sheets at the stated size are 2.4 m². Cutting is described as messy, with loose beads, and the sheets are called fragile next to denser foam. There is no fire class and no fixings. Use the pack for a thin lining, a craft job or packaging, and leave it when the floor or wall needs a real thickness.
Pros
Cons
Best for: You want a small, thin EPS sheet for a lining patch, packaging or a craft job.
Less suitable: A ground floor, a wet-room backer, or any job that needs 50 mm or a declared lambda.
Specifications
Common questions
Is the lambda a single declared figure?
No. The bullet prints Low (0.038–0.030 W/mK). That is a range. The listing does not give a kilopascal figure for EPS 70.
Does the printed coverage match the sheets?
The listing prints 2.58 square feet. Ten sheets at 600 × 400 mm are 2.4 m². Those two figures do not match.
Do the 4.6 stars measure only these 10 mm sheets?
The star line is 4.6 from 345 and the United Kingdom review text matches the 50 mm pack. A line about 7 mm sheets is on the listing, but it does not say which pack that reviewer bought.
Part TP15 is one foam tile backer, 1250 × 600 × 15 mm, covering 0.75 m², at £15.99. The bullet states the same 0.027 W/mK as the 40 mm board, and the heating mat is still not in the box. Across 349 amazon.co.uk reviews the line is 4.5, shared with the thicker sibling, so a comment about a very thin board for a skirting is not proof of this thickness. Reviewers use it on shower walls, on window reveals where insulated plasterboard was too thick, and as a light tile base they cut with a Stanley knife. Fixings and adhesive are a repeated extra purchase, and damaged corners appear in the same review block. The listing claims waterproofing for a wet area and does not name a tanking standard. It is the best value of the two boards that print 0.027 W/mK, when 15 mm is enough depth. It is the wrong board if the build-up needs 40 mm, or if the floor has to meet 0.18 W/(m²·K) on its own.
Pros
Cons
Best for: You want the cheaper of the two boards that print 0.027 W/mK, and 15 mm is enough for the tile build-up.
Less suitable: A 40 mm build-up, a floor U-value calculation, or a job that needs the foam type named.
Specifications
Common questions
Is a heating mat in the box?
No. The bullet says the 15 mm board suits electric underfloor heating mats and under-tile cable. The mat is not listed in the box. The part number on the listing is TP15.
Is this sold as a wet-area board?
The bullet claims waterproofing for a wet area and heavy wall tiles if the correct method is followed. No tanking standard is named, and reviews describe screws, washers and adhesive bought separately.
Are the 349 reviews only for 15 mm?
The star line is 4.5 from 349 and the United Kingdom review text matches the 40 mm board. A 6 mm comment in that block is not a measurement of this 15 mm board.
This is one foam tile backer, 1250 × 600 × 40 mm, covering 0.75 m², at £20.89. The bullet states 0.027 W/mK, and the material field only says Foam, so the page does not tell you whether the core is XPS, EPS or another foam. The star line is 4.5 from 349, and the United Kingdom review text matches the 15 mm board, including a 6 mm comment that is not a measurement of this 40 mm sheet. Reviewers describe shower walls and floors once the board is squared, taped, sealed and tiled, and they cut it with a Stanley knife. Adhesive, washers, screws, tape and a heating mat are not in the box. Broken edges show up in that shared block, including one order where four of ten boards arrived damaged. No Euroclass is printed. You take the extra thickness when 15 mm is too thin for the build-up, and you leave it when the same stated lambda at £15.99 is enough.
Pros
Cons
Best for: You want a 40 mm wet-room backer and you will buy the fixings, adhesive and heating mat separately.
Less suitable: A build-up that only needs 15 mm, or a floor that has to be shown against a U-value.
Specifications
Common questions
Is a heating mat in the box?
No. The bullet says the board is for wet areas with electric underfloor heating. Adhesive, washers, screws, tape and a heating mat are not listed.
Is this sold as a wet-area board?
The bullet claims waterproofing for a wet area and says the board will accept heavy wall tiles if the correct method is followed. No tanking standard is named.
Are the 349 reviews only for this 40 mm board?
The star line is 4.5 from 349 and the United Kingdom review text matches the 15 mm board. A 6 mm comment in that block is not a measurement of this 40 mm board.
One blue XPS board, 1200 × 600 × 10 mm, covers 0.72 m² and costs £7.99. The listing gives no lambda and no BS EN 13164 or BBA number, so a bullet about a lower electricity bill has no figure behind it. The amazon.co.uk line is 4.2 from 123 reviews, and many of the United Kingdom reviews are model-making rather than floors. One reviewer put a board under laminate on a cold concrete floor and said the room felt warmer, and another used it on a summerhouse ceiling after finding a foil board hard to cut to size. More than one review reports boards arriving broken. The country of origin is China, and the heating mat is not included. At £7.99 it is the lowest price in the set, and it is not the best value, because you cannot check a floor from a missing lambda. It belongs in a thin underlay conversation or a craft job, not where a floor limit of 0.18 W/(m²·K) has to be shown.
Pros
Cons
Best for: You want a single 10 mm XPS sheet as a thin underlay or a small craft board, and you do not need a lambda.
Less suitable: Any floor that must be checked against 0.18 W/(m²·K), or a buyer who needs a declared conductivity.
Specifications
Common questions
Does the listing give a lambda?
No. Thermal conductivity is not on the listing, and there is no BS EN 13164 or BBA number. A bullet about a lower electricity bill has no figure behind it.
Is a heating mat included?
No. The bullet says the board supports electric underfloor heating on solid base floors. The mat, adhesive and foil are not listed. Coverage is 0.72 m², which matches 1.2 m × 0.6 m.
What do the United Kingdom reviews actually cover?
The listing is 4.2 from 123 reviews. Several describe model-making rather than floors, and more than one reports boards arriving broken. Country of origin is China.
Shelf prices and stars are the amazon.co.uk snapshot of 21 October 2026 already stored for these five listings. This is not a laboratory test. The score starts from the star line and the review count, then a cut for what the listing cannot show. A named thickness, a stated lambda, and coverage that matches the sheet size can hold a score up. Shared review text, a lambda printed only as a range or missing, a coverage field that does not match the sheets, no Euroclass, fixings missing from the box, a 10 mm sheet also sold for craft, breakage in the reviews, and a bill-saving bullet with no figure are cuts. A layer resistance is not scored as a floor U-value. The highest score is the top pick. Best value is a different listing.
Amazon stars and review count
35%The base is the amazon.co.uk star line and review count, scaled. Shared review text does not count as a separate test of every thickness.
Thickness, lambda and coverage
25%A named thickness, one stated lambda, and a coverage figure that matches length times width times count can hold a score up. A range, or a missing lambda, cannot.
Listing limits
25%Cuts cover no Euroclass, fixings missing from the box, a 10 mm sheet also sold for craft, breakage in the United Kingdom reviews, and a bill-saving bullet with no figure.
Price for the stated job
15%Value is the price for a job the listing actually supports. The lowest price does not take the value award when lambda is missing. The value award is not the top pick.
Buy the element before the pack size. An insulation slab is a rigid board for a floor, a wall, a roof or a wet room. Match thickness, a declared lambda, the grade and the fire class to that element. A star rating does not replace a lambda. A layer resistance is not the U-value of the finished floor, and these five listings are not shown here as meeting Approved Document L.
An insulation slab is a rigid board: PIR, phenolic, EPS, XPS or mineral wool. Rolls, mats, blankets and edge tape are outside this category. UK buyers use slabs on floors, walls, roofs and wet rooms. The useful board matches that element in thickness, lambda, grade and fire class. Quality is a declared lambda, not a star rating. Branded PIR is often about 0.022 W/mK, EPS about 0.030–0.038, XPS about 0.033–0.036, and some phenolic boards about 0.019.
EPS 70 is a compressive class. The 50 mm pack is 50 mm thick. The listing does not print a kilopascal figure of its own.
A 10 mm sheet is an underlay or a craft board. Layer resistance is not the floor’s U-value, and a missing lambda cannot be checked against 0.18 W/(m²·K).
The two EPS packs share one review text and 4.6 from 345. The two tile backers share one text and 4.5 from 349. A 6 mm or 7 mm sentence is not a measurement of every thickness.
Name the element and the nation first. A shed, a ground floor and an external wall over 11 m follow different rules. Then read lambda and thickness together. Resistance of a layer is thickness in metres divided by lambda. 50 mm at 0.022 W/mK is about 2.27 m²K/W, and 50 mm at 0.038 is about 1.32. Neither figure is the floor’s U-value. England’s Approved Document L (2026) limits new-dwelling elements, including floor 0.18 W/(m²·K).
Read the facing, the fire class and the box before the stars. No Euroclass is printed on these five listings, so none is shown here as non-combustible or as A2-s1, d0. Over 11 m, the English prescriptive route expects A2-s1, d0 or better, or a BS 8414 / BR 135 test. A typical PIR datasheet class is Euroclass F, which must be kept dry. Mineral wool is A1 only when that datasheet says so. The tile backers include no heating mat, and reviews say fixings and adhesive are extra.
Three typical situations, each with a recommendation from this comparison.
You are lining a small outbuilding and 50 mm is the depth you can fit. The Triplast EPS 70 50 mm six-pack is the top pick at about £47.59: six sheets, 1200 × 600 mm, score 74, 4.6 from 345 reviews. The lambda is a range, and the review text is shared with the 10 mm pack. It is the wrong board when the floor must meet 0.18 W/(m²·K).
You want a foam tile backer and 15 mm is enough. The Thermopanel 15 mm board is best value at about £15.99, with a stated 0.027 W/mK and 4.5 from 349 reviews. Adhesive, washers and the heating mat are not in the box. The review text is shared with the 40 mm board. It will not show a floor U-value on its own.
15 mm is too thin for the build-up, and you will buy the fixings and the heating mat yourself. The Thermopanel 40 mm board is 1250 × 600 mm at about £20.89, score 72, with the same stated 0.027 W/mK. It does not take the value badge. Damaged corners appear in the shared reviews. It is still not a calculated floor.
The top pick is the Triplast EPS 70 50 mm six-pack at about £47.59. It scores 74, the highest here: six square-edged sheets, 1200 × 600 × 50 mm, 4.6 from 345 reviews. The lambda is a range, 0.030–0.038 W/mK, the review text is shared with the 10 mm pack, and no fire class is printed. Best value is the Thermopanel 15 mm tile backer at about £15.99. It scores 72, with a stated 0.027 W/mK and 4.5 from 349 reviews, the same stated lambda as the 40 mm board at about £20.89. The EkoBoard 10 mm XPS board at about £7.99 is the lowest price and does not take the value badge, because the listing has no lambda.
Triplast EPS 70 50 mm six-pack
Highest score at 74: the only 50 mm wall-and-floor sheet, 4.6 from 345 reviews, at about £47.59. The lambda stays a range.
Thermopanel 15 mm tile backer
About £15.99 with a stated 0.027 W/mK and 4.5 from 349 reviews. The 40 mm board prints the same lambda at about £20.89.
Editorial
Peter F. is the editor for DIY & tools at productscompared.co.uk. Comparisons in this category are checked against amazon.co.uk listings, review evidence and public UK sources.
Guides on what to look for, how to use a product, and common mistakes.
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.
This page contains affiliate links to amazon.co.uk (tag pcuk26-21). If you buy through them, we may earn a commission at no extra cost to you. Prices, stars and review counts are the amazon.co.uk figures already stored for this set. This is not a laboratory test.
