Celotex insulation review: what happened to the brand

Quick answer: Celotex no longer exists as a brand. The range is sold as Sopratherm by Soprema, with the same product codes and the same specifications. GA4000 is still 0.022 W/mK PIR, still Euroclass F, and 100mm costs £39.65 ex VAT for a 2.88m² sheet, checked 27 July 2026.

The name change, and why it matters to you

Saint-Gobain sold its UK PIR insulation business to the French group Soprema. Soprema folded Celotex in with an earlier acquisition, YBS Insulation, under one identity. The Celotex name has gone and Sopratherm replaced it. Soprema’s listing for the flagship board now reads SOPRATHERM GA4000 (previously Celotex GA4000).

Nothing else changed. Product codes are the same, U-values are the same, fire ratings are the same, installation is the same. The old celotex.co.uk product pages now redirect to soprema.co.uk. If a merchant quotes GA4000 and the boards turn up in Soprema livery, that isn’t a substitution.

We haven’t tested these boards. This is a read of published data sheets, BBA certificates and merchant pricing, checked 27 July 2026.

The range and what it costs

Three families, split by thickness rather than application, which is the sensible way round for a general purpose PIR board.

Watch the jump past 150mm. The rate per 100mm of depth runs at about £13.80 up to 150mm and about £18.80 at 200mm, because the thick boards are made in much smaller volumes. So if a specification calls for 180mm, two layers of 90mm cross-lapped is usually cheaper. It closes the joints better anyway.

Specification

• Declared thermal conductivity 0.022 W/mK across GA4000
• Board size 2400 x 1200mm as standard, foil faced both sides
• Reaction to fire Euroclass F to BS EN 13501-1
• BBA certificate 25/7318 for pitched roof, dry lining and floor insulation
• Soprema tells specifiers not to use it in the external walls of relevant buildings over 11 metres

Euroclass F is the bottom rung. In a house that mostly means the board needs a lining between it and the room, normally 12.5mm plasterboard, and it shouldn’t be left exposed in a loft or garage. The insulation fire safety guide covers what that means for a domestic build-up.

The history nobody should skip

Celotex RS5000 was the insulation used across most of the Grenfell Tower cladding system. The Grenfell Tower Inquiry’s phase 2 report, published on 4 September 2024, found that in trying to break into the high-rise market Celotex “embarked on a dishonest scheme to mislead its customers and the wider market” (volume 1, paragraph 2.28). It found the 2014 BS 8414 test had been run with fire-resistant magnesium oxide boards in critical positions, and that the test report Celotex then obtained left them out.

In February 2025 the government announced investigations under the Procurement Act 2023 into seven organisations, including Saint-Gobain Construction Products UK Limited in relation to the actions of Celotex Limited, which it owned at the relevant time. Those investigations were paused in July 2025 to avoid cutting across criminal investigations. No debarment decision has been reached.

RS5000 was a high-rise facade product. It isn’t in the current range. The boards in the table above are ordinary general purpose PIR sold for floors, pitched roofs and dry lining, governed by the same standards as every other PIR board on the market. The record is here because it’s a matter of public inquiry finding, not because it says anything about a floor board in a bungalow.

Is it the right board for you?

On price it’s the best of the mainstream PIR brands. At £13.77 per square metre for 100mm against Kingspan Thermapitch at £18.56, you’re getting the same published 0.022 W/mK for about a quarter less. If a builder offers you Kingspan Therma and Sopratherm at the same rate, take the Kingspan and pocket the brand. And if you’re buying the boards yourself, buy on price.

Where it’s the wrong choice: a cold loft with clear headroom, where a glass wool roll at £2.32 per square metre does the same job for a fraction of the money, and anywhere the material would be left exposed. Compare the options in mineral wool, PIR and EPS compared and check the thickness maths in U-values explained.

For a modelled whole-job figure rather than board prices, use the cost calculator or the insulation product guide, both built on our £1,498 mid estimate for a typical insulation job.

FAQs

Is Sopratherm the same as Celotex?

Yes. Same factory, same product codes, same published specifications. Soprema bought the business from Saint-Gobain and retired the Celotex name. GA4000, XR4000 and TB4000 stayed on as product references, and celotex.co.uk redirects to Soprema.

What is the thermal conductivity of Celotex GA4000?

0.022 W/mK, declared to BS EN 13165. That’s standard for a foil-faced PIR board. A 100mm sheet gives roughly 4.5 m²K/W of resistance on its own, before you count any other layer in the construction.

Can Celotex boards be used in a wall?

In a domestic cavity or as internal dry lining, yes, with a lining board between the insulation and the room. England’s regulation 7(2) excludes Euroclass F from the external walls of relevant buildings 18 metres and over, and Soprema’s own advice is to keep GA4000 out of external walls above 11 metres.