Best insulation brands in the UK for 2026

Quick answer: For loft rolls, Knauf and Superglass are cheapest per square metre: about £2.32 and £2.70 at 100mm ex VAT, trade, checked 27 July 2026. For thin walls and floors, Kingspan Kooltherm phenolic at 0.019 W/mK needs the least depth. Rockwool costs far more but wins on fire and sound.

How we compared them

We haven’t tested any of these products. This is a read of published technical data, merchant pricing and certification, all checked on 27 July 2026. Insulation is one of the few building products where the number that decides the outcome is printed on the packaging. So a desk comparison gets you most of the way there.

Three things drive the ranking. Declared thermal conductivity, written as lambda in W/mK, because it sets how thick the layer has to be. Price per square metre at the thickness you need, not the headline pack price. And reaction to fire, which in some walls decides whether you’re allowed the material at all.

We looked for Trustpilot scores on all five manufacturers. Nothing usable. They sell through builders’ merchants, so the review pages that exist belong to the merchants, and a distributor’s delivery times tell you nothing about stone wool.

The five brands at a glance

That table is the whole argument. Phenolic insulated plasterboard costs roughly ten times a glass wool roll per square metre and gives well over twice the performance per millimetre. Worth it? Only if you’re short of space.

Kingspan

Kingspan Insulation is the British arm of Kingspan Group, listed in Dublin. Two ranges matter to homeowners. Kooltherm is phenolic foam, and Kingspan declares 0.019 W/mK for the core of the K118 insulated plasterboard and the K106 cavity board. About as low as lambda goes on a merchant shelf. Therma is ordinary PIR at 0.022 W/mK, sold as Thermapitch TP10 for roofs, Thermafloor TF70 for floors and Thermawall TW55 for walls.

Kooltherm carries a heavy premium. K106 cavity board at 90mm works out around £41 per square metre at Trade Insulations, against £13.77 for a 100mm Sopratherm PIR sheet. Buy it when depth is genuinely tight, such as internal wall lining in a small terrace where every 10mm of room width counts. Read our full Kingspan insulation review for the detail on fire classification and the Grenfell Inquiry findings.

Celotex, now Sopratherm

This one has changed underneath people. Saint-Gobain sold the Celotex PIR business to the French group Soprema and the Celotex name has gone. The range is Sopratherm now, same product codes: Soprema’s listing reads SOPRATHERM GA4000 (previously Celotex GA4000). If a merchant quotes GA4000 and delivers a board in Soprema livery, it’s the same board.

GA4000 sits at 0.022 W/mK, standard for PIR, in 50mm to 100mm. XR4000 covers 110mm to 200mm. TB4000 covers thin work from 20mm. All are Euroclass F, the bottom of the reaction-to-fire scale. England’s ban on combustible materials in external walls, regulation 7(2), bites at 18 metres. Soprema goes further and tells specifiers to keep GA4000 out of external walls above 11 metres. Our Celotex insulation review covers the rebrand and the regulatory history.

Rockwool

Stone wool, not glass wool, and the difference shows up in density. RWA45 runs at 45 kg/m³ against roughly 10 to 12 for a loft roll. That density is why it deadens sound between rooms, holds its shape in a stud wall without sagging, and reads Euroclass A1 for non-combustibility. Rockwool says its stone wool lasts at least 50 years with no loss of performance, based on testing products recovered during the renovation of an airport hangar in Copenhagen.

It isn’t the loft answer for most people. A Rockwool Twin Roll at Bradfords is £68.36 ex VAT for 6.6m² at 100mm, more than four times a glass wool roll, for the same 0.044 W/mK. Buy it for party walls, stud partitions and anywhere you want fire performance rather than depth. See the Rockwool insulation review.

Knauf

Knauf Insulation is the cheapest way to hit a decent loft U-value in Britain, and it has been for years. Loft Roll 44 at 100mm is £32.24 ex VAT for a 13.89m² pack, which is £2.32 per square metre. DriTherm Cavity Slab 32 at 0.032 W/mK is the strong full-fill cavity product, water-repellent treated so moisture doesn’t track across the cavity, and BBA certificate 95/3212 covers all exposure zones.

One naming quirk trips people up. Knauf dropped the Earthwool brand name, but merchants still list products as Earthwool. There’s no product difference. The Knauf insulation review has the full range and the retail versus trade price gap, which is large.

Superglass

Made in Stirling, and since June 2023 owned by the Belgian group Etex, which also owns Ursa. Multi-Roll 44 is the loft product: 0.044 W/mK, Euroclass A1, up to 84% recycled waste glass, and a CCPI assessment mark verifying that the published data is accurate.

On performance it’s a straight match for Knauf. On price it usually sits a fraction above: £2.70 per square metre at 100mm at Roofing Outlet, against Knauf’s £2.32. So buy whichever your merchant stocks. Details in the Superglass insulation review.

Which brand for which job

If you want one answer, it’s Knauf. Loft Roll 44 at £2.32 per square metre does the job in four lofts out of five, and anything dearer needs a reason you can name out loud. Job by job:

• Cold loft, joists exposed, plenty of headroom: Knauf or Superglass glass wool at 270mm. Cheapest route to the current standard. See loft insulation thickness.
• Room in roof or loft conversion where depth between rafters is fixed: Kingspan Therma or Sopratherm PIR, or Kooltherm if the rafter depth is really tight.
• Full-fill cavity: Knauf DriTherm 32, or Rockwool full-fill batts if the exposure rating worries you.
• Stud partitions and party walls where sound is the point: Rockwool RWA45 or Flexi.
• Internal wall lining in a small room: Kingspan Kooltherm K118 insulated plasterboard, purely because it steals the least floor area.

What brand doesn’t change

Nobody’s insulation works when it’s fitted badly. A 0.019 W/mK board with a 5mm gap round the edge performs worse than a well-fitted glass wool roll, because the air path round the edge dominates. Our guide to U-values and insulation performance shows why the sums fall apart once you allow for gaps and thermal bridging.

Watch the VAT too. Insulation is zero rated to 31 March 2027, but only when a supplier installs it. HMRC’s Notice 708/6 is blunt about this: the sale of energy-saving materials by a retailer is always standard rated. Buying rolls yourself at a merchant means paying 20% on top of every price in this article.

For a modelled cost of the whole job rather than material prices, our cost calculator and insulation product guide work from a £2,950 mid estimate for loft and cavity wall insulation, based on Energy Saving Trust installed prices and adjusted by region. Method in how we calculate costs.

FAQs

Is an expensive insulation brand worth it?

Only when depth is limited. Phenolic at 0.019 W/mK gets you the same U-value in well under half the thickness of glass wool at 0.044, and costs around ten times as much per square metre. In an open loft with 300mm of clear space, that trade makes no sense at all.

Do any of these brands offer a warranty to homeowners?

Not in the way a boiler manufacturer does. These are materials sold through merchants, covered by BBA certificates and BS EN 13162 or 13165 product standards rather than a consumer guarantee. The workmanship warranty, if you get one, comes from whoever installs it.

Which brands are non-combustible?

Rockwool, Knauf glass wool and Superglass all carry Euroclass A1. Kingspan Therma and Sopratherm PIR are Euroclass F. Kingspan Kooltherm K118 is B-s1,d0. See insulation fire safety for what those classes mean in a house.