Stone Wool vs Glass Wool Insulation: Rockwool vs Knauf, Isover and URSA
"Mineral wool" covers two different products: stone wool (Rockwool is the best-known brand) and glass wool (Knauf Insulation, Isover, URSA and ODE). Both are non-combustible, both absorb sound and both are used in lofts, stud walls, floors and cavities. But they're made differently, sold in different formats and priced differently. This guide compares them product by product using manufacturer data, so you can pick the right one for the job.
Quick answer
- Glass wool is usually the cheaper way to fill a loft, a stud partition or a cavity. It's light, comes compressed in rolls and covers a lot of area per pack.
- Stone wool is denser and comes mostly as rigid or semi-rigid slabs. It holds its shape in walls and floors, cuts cleanly and is popular for acoustic and fire-stopping work.
- Both are Euroclass A1 (non-combustible) in every product listed below, according to the manufacturers.
What's the difference?
Stone wool is made by melting volcanic rock (mainly basalt) and spinning it into fibres. Glass wool is made the same way from sand and recycled glass. Glass wool fibres are longer and springier, which is why it compresses well into rolls. Stone wool is generally made at higher densities and sold as slabs that stand up between studs without slumping.
Thermal performance compared
Lower λ (lambda) means better insulation per millimetre. Figures are from each manufacturer's datasheet:
| Product | Type | Format | λ (W/mK) | Fire |
|---|---|---|---|---|
| Rockwool Flexi | Stone wool | Slab with flexible edge | 0.038 | A1 |
| Rockwool RWA45 | Stone wool | Acoustic slab | 0.035 | A1 |
| Knauf Insulation Loft Roll 44 | Glass wool | Roll | 0.044 | A1 |
| Knauf Insulation DriTherm 32 | Glass wool | Cavity slab | 0.032 | A1 |
| URSA ACOUSTIC ROLL | Glass wool | Partition roll | 0.035 | A1 |
| URSA FRAMETEC 32 | Glass wool | Framing roll | 0.032 | A1 |
So neither type always wins on thermal performance: it depends on the product's density. A dense glass wool like DriTherm 32 or FRAMETEC 32 (λ 0.032) actually beats both Rockwool slabs here. If thickness is tight, PIR board (λ 0.022) insulates far better than any wool. See what thickness of PIR insulation do I need.
Acoustic partitions: stone wool slab vs glass wool roll
For a stud wall between rooms, the most common choices are a stone wool slab like Rockwool RWA45 or a glass wool partition roll like URSA ACOUSTIC ROLL, Isover APR 1200 or ODE Lunaflex APR HP. All of them fill the void and soak up sound. In practice, the sound insulation of the finished wall depends at least as much on the plasterboard (one or two layers, standard or acoustic) and on sealing gaps as on which wool you use. Our stud wall soundproofing guide walks through a full build-up.
| Product (thickness) | Pack | Price | Per m² |
|---|---|---|---|
| Rockwool RWA45 50mm | 6.48m² | £28.03 | £4.33 |
| Rockwool RWA45 100mm | 2.88m² | £25.18 | £8.74 |
| URSA ACOUSTIC ROLL 50mm | 14.4m² | £39.48 | £2.74 |
| URSA ACOUSTIC ROLL 100mm | 7.2m² | £28.74 | £3.99 |
| Isover APR 1200 50mm | 15.6m² | £58.48 | £3.75 |
| ODE Lunaflex APR HP 50mm | 12m² | £29.90 | £2.49 |
Prices are ex VAT, at the time of writing.
Which to use where
- Lofts: glass wool rolls, laid between and over the joists. See the 270mm rule and our loft insulation.
- Stud partitions: either. Glass wool rolls are usually cheaper per m²; stone wool slabs stand up on their own and are easier to fit around services. Browse Rockwool acoustic slabs and glass wool.
- Timber frame walls: a dense framing roll like FRAMETEC 32, or Rockwool Flexi slabs, which have a flexible edge that springs into the frame.
- New-build cavity walls: a water-repellent full-fill cavity slab such as Knauf Insulation DriTherm 32.
Frequently asked questions
Is Rockwool the same as mineral wool?
Rockwool is a brand of stone wool, which is one type of mineral wool. Glass wool is the other.
Is stone wool more fire resistant than glass wool?
Every stone wool and glass wool product in this guide is rated Euroclass A1 (non-combustible) by its manufacturer. Stone wool has a higher melting point, which is why it's often specified for fire-stopping details, but for normal walls, lofts and floors both meet A1.
Which is better for soundproofing?
Both work well in a stud wall. Denser stone wool slabs are often chosen for acoustic work, but the plasterboard and airtightness of the wall make the biggest difference.
Can I mix stone wool and glass wool?
Yes. For example, many people use glass wool rolls in the loft and Rockwool slabs in internal partitions.
Order mineral wool insulation
Use our insulation calculator to work out how many packs you need. Prices are shown ex VAT. We are delivery only (no collection) and deliver to mainland England. Insulation, plasterboard and drylining orders have a £400 ex VAT minimum and free delivery (see delivery information). Call us on 03330 908479 (Mon–Thu 8am–5pm, Fri 8am–12pm), email sales@insulationwarehousedirect.co.uk, or order online.
Sources: Rockwool Flexi and Rockwool RWA45 product pages and datasheets; Knauf Insulation Loft Roll 44 and DriTherm Cavity Slab 32; URSA ACOUSTIC ROLL and URSA FRAMETEC 32. Figures are indicative and correct at the time of writing.