Mineral wool is the UK's most common insulation, and for good reason: it is affordable, easy to fit and safe. This independent guide explains the difference between glass wool and rock wool, how it performs, where it wins, and what it costs, so you can decide whether it is right for your job.
By Adam Gough, Founder & Lead Adviser, Insulation Advice Centre
Last reviewed: 18 August 2026. Typical lambda values are published manufacturer and CIBSE figures; check your product's declared value. Costs are Checkatrade (2026). Guide only, not a quote.
Takes under 60 seconds. No cost, no obligation.
Mineral wool is the material most UK homeowners picture when they think of insulation: the soft, fibrous rolls and slabs found in millions of lofts. It is made by spinning molten glass or rock into fibres, and it comes in two main forms. Both insulate well, are non-combustible and are relatively cheap, which is why mineral wool is the default choice for so many jobs. This guide explains where it is the right choice, and where a different material earns its place instead.
The two types are similar but not identical:
For a straight loft-floor job, glass wool is usually the most cost-effective. Where you also want acoustic or fire benefits, rock wool is worth the small premium. See how they line up against rigid boards in our mineral wool vs Rockwool vs PIR comparison.
With a lambda of around 0.038 to 0.040, mineral wool needs more thickness than a rigid board to reach the same U-value, but that is rarely a problem in a loft where there is depth to spare. Laid to the Energy Saving Trust's recommended 270mm on a loft floor, mineral wool reaches roughly a U-value of 0.14 W/m2K, comfortably inside the sort of target current Building Regulations expect for a loft (verify against the current regulations for your project). Where space is tight, such as a roof slope in a loft conversion, a lower-lambda board like PIR reaches the target in less depth, which is the main reason to pay more for it. You can check any build-up with our free U-value calculator.
Where it is less suitable: very tight spaces with little depth (a board is usually better there), or applications needing a rigid, load-bearing layer. As always, the honest rule is best for this application, because of these conditions, not best overall.
Mineral wool is usually the cheapest insulation to buy. As a sourced guide:
| Item | Typical UK figure | Source |
|---|---|---|
| Mineral wool quilt, material only | Around £10 per m² | Checkatrade, 2026 |
| Insulating an uninsulated loft to 270mm | Around £750 (Great Britain) | Energy Saving Trust, 2026 |
| Per property, 270mm quilt (installer cost) | Roughly £654 terraced, £825 semi, £1,206 detached | Checkatrade, 2026 |
For the full cost picture across materials and house types, see our loft insulation cost guide and insulation cost overview. Always compare a few quotes rather than accept the first.
Mineral wool is cheapest and easy to fit but needs depth. PIR costs more but reaches the same U-value in about half the thickness, which matters where space is tight. Multifoil is a different animal again, judged on its tested build-up rather than a simple lambda, and useful only in very tight spaces installed exactly as tested. For the full side-by-side, see our insulation comparison, and for loft-specific advice our loft insulation guide.
If mineral wool looks right for your job, or you are weighing it against a board, we can help you decide and match you with vetted, accredited installers so you can compare no cost quotes side by side. Tell us about your project in under a minute, or call us free on 0800 4947163.
The questions UK homeowners ask us most about mineral wool.
Both are mineral wool. Glass wool is spun from glass, is lighter and usually cheaper, with a typical lambda around 0.040. Rock wool is spun from volcanic rock (the basis of brands like Rockwool), is denser with a slightly lower lambda around 0.038, and offers better fire resistance and sound insulation. Glass wool suits budget loft jobs; rock wool suits walls and anywhere fire or acoustics matter.
The Energy Saving Trust recommends around 270mm on a loft floor. At a lambda of about 0.040 that reaches roughly a U-value of 0.14, inside the sort of target current Building Regulations expect; verify against the current regs for your project. There is usually plenty of depth in a loft to lay this cheaply.
It depends on the job. Mineral wool is cheaper and easy to fit but needs more thickness. PIR costs more but reaches the same U-value in about half the depth, so it wins where space is tight, such as a roof slope. For a standard loft floor with room to spare, mineral wool is usually the better value.
The material is usually the cheapest option, around 10 pounds per square metre (Checkatrade, 2026). Insulating an uninsulated loft to 270mm is around 750 pounds (Energy Saving Trust), or by property roughly 654 pounds terraced, 825 semi and 1,206 detached (Checkatrade). Compare a few quotes.
Mineral wool is non-combustible, which is one of its advantages, and rock wool in particular has strong fire performance. Standard precautions apply when handling it: wear gloves, a mask and long sleeves, as the fibres can irritate skin and airways during installation.
We will tell you straight if mineral wool is all your job needs, even though we supply and arrange certified SuperFOIL installations ourselves. Tell us about your project and we will help you weigh mineral wool against the alternatives, then match you with vetted, accredited installers so you can compare no cost quotes.
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