Mineral wool, Rockwool, PIR and multifoil each win in different situations. This independent comparison sets them side by side on performance, cost and best use, so you can decide by application rather than by marketing. We supply and arrange certified SuperFOIL installations, and we will still tell you if a different material suits your home better.
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.
There is no single best insulation. The right material depends on where it is going, how much space you have, your budget, and the standard you are trying to reach. The most common mistake we see is picking a product on a headline claim rather than matching it to the job. This guide compares the main UK options honestly, then helps you choose by application.
Thermal conductivity (lambda) matters because a lower lambda reaches the same U-value in less thickness. But lambda is not the whole story: cost, space, moisture behaviour and how a product is installed all count, and multifoil in particular cannot be reduced to a single lambda (more on that below).
| Material | Typical lambda (W/mK) | Relative cost | Best for | Main limitation |
|---|---|---|---|---|
| Mineral / glass wool quilt | ~0.040 | Lowest (around £10/m² material) | Cold-loft floors where there is depth to spare | Needs more thickness for a given U-value |
| Rock wool (e.g. Rockwool) | ~0.038 | Low | Lofts and walls where fire resistance and acoustic performance matter | Heavier; still needs depth |
| PIR board | ~0.022 | Higher (around £35/m² material) | Roof slopes, loft conversions and floors where space is tight | Costs more; rigid boards need careful fitting |
| Multifoil | Not a simple lambda; judged on tested build-up | Mid to higher | Very tight spaces where every centimetre counts | Needs air gaps and correct installation to perform |
| Loose-fill | ~0.040 | Low (around £12/m² material) | Awkward, irregular or hard-to-reach loft spaces | Can settle; less tidy around obstructions |
Lambda values are typical published figures and vary by product; always use the manufacturer's declared value for your U-value calculation. You can do that with our free U-value calculator.
Multifoil works differently from the others. A large part of its performance comes from reflecting radiant heat and from the air gaps it needs on either side, so it is tested as a whole build-up rather than as a bare material with a single lambda. That means you cannot fairly line it up against mineral wool or PIR on lambda alone, and you should never accept an "equivalent to 200mm" claim without the tested U-value of the exact build-up you will construct. Installed as tested, it can be genuinely useful where space is very tight; installed badly, it disappoints. Our honest multifoil insulation guide covers this in full.
Spray foam is a different case, which is why it is not in the table above. Applied to the underside of a roof it can perform, but it has become closely associated with problems at survey, mortgage and sale time, mainly because it can hide the roof timbers and, if the wrong type is used or ventilation is compromised, trap moisture. For that reason we treat it separately rather than recommending it alongside the mainstream materials. If it affects you, our guides to spray foam and your mortgage and spray foam removal cover it, and the National Spray Foam Advisory has an in-depth set of spray foam problems FAQs.
The honest answer is always "best for this job, because of these conditions." Here is how the choice usually falls:
For a deeper look at the specific match-ups homeowners ask about most:
Decide the application first, then shortlist the materials that suit it, then compare the tested performance and the total installed cost, not just the material price. Whatever you choose, installation quality matters as much as the product. When you are ready, we can 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 comparison questions UK homeowners ask us most.
There is no single best type; it depends on the application. Mineral wool quilt usually wins on a cold-loft floor where there is depth to spare. PIR board wins where space is tight, such as a roof slope or loft conversion, because its lower lambda reaches the same U-value in less thickness. Multifoil can suit very tight spaces if installed exactly as tested. Choose by the job, not the brand.
Not always; it depends on space and budget. PIR has a much lower lambda (around 0.022 vs 0.040 for mineral wool), so it achieves the same U-value in roughly half the thickness, which is valuable where headroom is limited. But it costs more per square metre, so for a standard loft floor with room to spare, mineral wool is usually the better value.
It can in the right, very tight application, but you must judge it on the tested U-value of the exact build-up, including the air gaps it needs, not on an "equivalent to 200mm" claim. Its performance depends heavily on correct installation, which is why it must be compared as a whole build-up rather than by a single lambda value.
Mineral wool quilt is usually the cheapest material (around 10 pounds per square metre), with loose-fill close behind. PIR board costs more (around 35 pounds per square metre). But compare the total installed cost for your job, not just the material price, and always get more than one quote.
Use each product's declared lambda and your build-up to work out the U-value, then compare against the target for your application. Our free U-value calculator does this for mineral wool, PIR and similar materials. Multifoil is the exception, as it is rated as a tested build-up rather than by lambda.
We will give you a straight answer either way: we supply and arrange certified SuperFOIL installations, and we will still tell you if a different option suits your home better. Tell us about your home and we will help you weigh the options, then match you with vetted, accredited installers so you can compare no cost quotes.
Get My No Cost Quotes Now →Loft insulation · PIR insulation · Mineral wool insulation · Mineral wool vs Rockwool vs PIR · Multifoil insulation · U-values explained · U-value calculator · Insulation costs · Find installers
Insulation Advice Centre