Kingspan insulation review: Kooltherm and Therma boards

Quick answer: Kingspan sells two ranges. Kooltherm phenolic at 0.019 W/mK is about as thin as mainstream insulation gets and costs around £25 per square metre for 37.5mm insulated plasterboard. Therma PIR at 0.022 W/mK is £18.56 per square metre at 100mm. Both prices ex VAT, Trade Insulations, checked 27 July 2026.

What Kingspan actually sells

Kingspan Insulation is the British arm of Kingspan Group plc. For domestic work the range splits cleanly in two, and the split matters more than the product codes suggest.

Kooltherm is phenolic foam with a fibre-free rigid thermoset core. Kingspan publishes 0.019 W/mK for the insulation core of both the K118 insulated plasterboard and the K106 cavity board. That is about as low as lambda goes in a mainstream board. Therma is ordinary PIR at 0.022 W/mK, sold under three names for three jobs: Thermapitch TP10 for pitched roofs, Thermafloor TF70 for floors and Thermawall TW55 for walls. The boards are near enough identical apart from the facings.

We haven’t tested these boards. Everything here comes from published specifications, BBA certificates and merchant pricing, checked 27 July 2026.

What it costs

Look at the K106 line. Ninety millimetres of Kooltherm cavity board is £41.47 per square metre. A 100mm Sopratherm PIR sheet doing a similar thermal job is £13.77. You’re paying roughly three times over for about 14% better lambda, which buys you a thinner cavity. In a new build with a fixed 100mm cavity that can be the difference between passing and failing. In a retrofit it usually isn’t.

Fire classification and where boards are allowed

Kingspan Therma PIR is Euroclass F, the bottom of the BS EN 13501-1 reaction to fire scale, and Thermapitch TP10 carries BBA certificate 14/5133. Kooltherm K118 does considerably better at B-s1,d0, largely because of the plasterboard bonded to its face. The bare K106 cavity board is Euroclass F, same as the PIR.

Neither can go in the external wall of a relevant building 18 metres or higher in England, under regulation 7(2) of the Building Regulations 2010. For a two-storey house none of this applies directly. But it tells you something about the material: PIR burns, produces a lot of smoke, and needs a plasterboard lining between it and the room. Our guide to insulation and fire safety for UK homeowners sets out the practical rules.

The Grenfell findings

Any honest review of Kingspan has to deal with this. The Grenfell Tower Inquiry’s phase 2 report was published on 4 September 2024. On Kingspan’s K15 phenolic board it concluded that the story of its development and marketing for use on buildings over 18 metres between 2006 and 2019 is “one of deeply entrenched and persistent dishonesty” on Kingspan’s part in pursuit of commercial gain (phase 2 report, volume 2, paragraph 22.134). K15 made up a small part of the insulation on the tower.

Kingspan’s published statement on the report, checked 27 July 2026, acknowledges what it calls wholly unacceptable historical failings in part of its UK insulation business and says they were in no way reflective of how the group conducts itself. It also points to the report’s finding that the type of insulation was immaterial to the fire spread, which the inquiry attributed to the PE ACM cladding, a product Kingspan did not make.

In February 2025 the government announced investigations under the Procurement Act 2023 into seven organisations including Kingspan Insulation Limited, to establish whether they had engaged in professional misconduct. Those investigations were paused in July 2025 so as not to cut across the criminal investigation. No debarment decision has been made.

None of that touches the products in this review. K15 was a high-rise facade board. Loft rolls, floor boards and insulated plasterboard in a house sit in a different regulatory world entirely. But if you’re choosing between two brands on equal specifications, some people will factor it in, and they’re entitled to.

Where Kingspan is worth the money

Buy Kooltherm when you’re short of millimetres and the millimetres cost you something. Internal wall lining in a Victorian terrace is the clearest case: K118 at 37.5mm gets you a usable improvement while stealing under 4cm from each wall, where mineral wool on battens would take 100mm or more. Our piece on phenolic foam insulation boards goes into the build-up.

Don’t buy Kooltherm for a cold loft. Nothing about an open loft rewards a thin material, and you’ll pay eight to ten times what a glass wool roll costs to save space you aren’t using. Therma PIR is the sensible middle: correct for rafter-level insulation in a loft conversion, correct under a solid floor, and about a third dearer than the equivalent Sopratherm sheet for identical published lambda.

That last point is the honest summary. On PIR, Kingspan is a price premium for a brand and a distribution network, not for performance. Compare specs in our guide to mineral wool, PIR and EPS, and check the maths in U-values explained. For whole-job costs, the calculator and insulation guide work from our modelled £2,950 mid estimate for loft and cavity wall insulation, based on Energy Saving Trust installed prices.

FAQs

Is Kooltherm worth the extra over Therma?

Only if depth is constrained. Kooltherm at 0.019 W/mK needs roughly 14% less thickness than Therma at 0.022 for the same resistance, and costs roughly twice as much per square metre. In a loft, floor or generous cavity, Therma or a competing PIR board is the better buy.

Does Kingspan insulation come with a guarantee?

Not a consumer warranty. The boards are covered by BBA certificates and manufactured to BS EN 13165. Kingspan publishes performance data and durability statements rather than a years-long guarantee to the homeowner. Any warranty on the job comes from the installer.

Can I use Kingspan PIR in a loft between joists?

You can, but cutting rigid board to fit between irregular joists leaves gaps that undo the benefit, and it costs several times more than a roll. Use rolls at ceiling level and save the board for rafter-level work where the depth is fixed.