Knauf insulation review: Loft Roll 44 and DriTherm

Quick answer: Knauf is the cheapest route to a good loft U-value in Britain. Loft Roll 44 at 100mm is £32.24 ex VAT for a 13.89m² pack, which is £2.32 per square metre, Euroclass A1 and 0.044 W/mK. DriTherm Cavity Slab 32 at 0.032 W/mK is the pick for full-fill cavities. Prices checked 27 July 2026.

First, the Earthwool confusion

Half the merchants in the country still sell Knauf products as Earthwool. Knauf discontinued the Earthwool name to simplify its brand and its range, and named products for the job they do instead. Merchants carried on using the old name, because that’s what customers search for.

There’s no product difference. A pack labelled Knauf Earthwool Loft Roll 44 and a pack labelled Knauf Loft Roll 44 are the same glass mineral wool with the same declared conductivity. If a quote lists Earthwool, you aren’t being sold old stock.

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

Loft Roll 44

The workhorse. Glass mineral wool, 0.044 W/mK, Euroclass A1 non-combustible, made with Knauf’s ECOSE bio-based binder rather than the phenol formaldehyde binder that gave old fibreglass its smell and its brown colour. Available in 100mm, 150mm, 170mm and 200mm. The rolls are part-perforated, so a 1200mm width splits into two 600mm or three 400mm strips to suit your joist spacing.

At £32.24 ex VAT for 13.89m² at 100mm, nothing in this market beats it on cost per square metre. Sale-priced Superglass gets close. That’s the entire competition. To reach the 270mm now treated as standard, you lay 100mm between the joists and 170mm across them at right angles. The loft insulation thickness guide covers why the cross layer matters more than the first one.

The retail price trap

This is the single most useful thing in this review. Knauf sells the same fibre through DIY sheds under the Space name, and the price gap is large.

Correct for thickness and VAT and the retail rolls still land roughly a quarter to a third dearer per square metre of equivalent depth. So if you’re doing a whole loft, open a trade account or buy from an online insulation merchant. If you need two rolls to finish a corner, the shed is fine.

One more VAT point. Insulation is zero rated until 31 March 2027, but HMRC’s Notice 708/6 restricts that to installation: the sale of energy-saving materials by a retailer is always standard rated. DIY buyers pay 20% either way.

DriTherm cavity slabs

Knauf’s strongest product is arguably not the loft roll. It’s DriTherm. The cavity slab comes in three grades, 32, 34 and 37, named after their conductivity. DriTherm 32 at 0.032 W/mK is the best glass wool lambda you’ll find for a full-fill cavity, and it’s close to EPS bead performance in a slab you can build against.

The slabs carry a water-repellent additive, so water crossing the outer leaf drips down the face instead of tracking through to the inner leaf. BBA certificate 95/3212 covers use as full-fill insulation in external masonry cavity walls up to 25 metres, in all exposure zones including very severe. And that last clause is the one to check if you’re anywhere on an exposed western coast.

If you’re choosing between full-fill slabs and blown bead, our comparison of mineral wool, PIR and EPS covers the trade-offs, and U-values explained shows what 0.032 versus 0.037 does to the finished wall.

The rest of the range

Two other Knauf products turn up in domestic quotes often enough to name. Acoustic Roll is a denser glass wool sold in 25mm to 100mm for stud partitions and between floors. It’s the cheap way to quieten a room if you’re already opening the plasterboard. Rocksilk is Knauf’s rock mineral wool line, which puts the company up against Rockwool on slabs and fire stopping.

Building Slab is the general purpose friction-fit product for timber frame and stud bays, and plenty of merchants still list it under an Earthwool heading. Check the thickness. Then check the width against your stud centres, because that’s what decides whether it stays put without fixings.

Where Knauf is the wrong choice

Anywhere depth is fixed. At 0.044 W/mK a loft roll needs about twice the thickness of a PIR board for the same resistance, so between 150mm rafters in a loft conversion it won’t reach a sensible U-value. Use board there.

Anywhere you want acoustic mass. Knauf makes acoustic rolls and Rocksilk rock wool slabs, but for a party wall or a stud partition, Rockwool RWA45 at 45 kg/m³ is the denser product and the one most acoustic specifications call for.

For everything else in a house with a normal loft, Knauf is the default and the burden of proof is on anything more expensive. Modelled whole-job costs are in the calculator and the insulation guide.

FAQs

Is Knauf Earthwool still made?

The product is, the name isn’t. Knauf dropped the Earthwool brand to simplify its range and named products for the job they do. Merchants still list Earthwool because that’s what people search for. The material inside the pack is unchanged.

What is ECOSE technology?

Knauf’s bio-based binder, used in place of the traditional phenol formaldehyde binder. It’s why the wool is brown rather than yellow or pink. It doesn’t change the declared thermal conductivity, which is 0.044 W/mK for Loft Roll 44 either way.

Is Knauf loft insulation fire rated?

Loft Roll 44 is Euroclass A1 to BS EN 13501-1, the highest reaction to fire classification, the same as Rockwool and Superglass. PIR boards sit at Euroclass F. More on what those classes mean in insulation fire safety.