Best Rock Wool Insulation 2026: Top UK Slabs for Sound & Heat
The best rock wool insulation for UK homes in 2026 is the Rockwool RWR105 100x400x1200mm, which delivers robust thermal and acoustic performance at £58.96.
Klara SandbergEditor-in-Chief & Home Electronics Expert ·
Klara leads the Testix editorial team and has over 9 years' experience testing and reviewing home electronics. With a background as a technology journalist for several UK publications, she has a sharp eye for what separates a good product from a mediocre one. At Testix, Klara is responsible for the overall quality of all published reviews and writes in-depth reviews of audio, visual and smart home products.
We examined 9 rock wool insulations and analysed over 1,450 customer reviews from Currys, John Lewis, Argos and Amazon UK. We evaluated thermal efficiency, soundproofing, fire safety, ease of installation and value for money. Prices range from £47.22 to £78, with models from Rockwool.
We examined 9 rock wool insulations and analysed over 1,450 customer reviews from Currys, John Lewis, Argos and Amazon UK. We evaluated thermal efficiency, soundproofing, fire safety, ease of installation and value for money. Prices range from £47.22 to £78, with models from Rockwool.
Top List5 best rock wool insulations 2026
Best Rock Wool Insulation 2026
#1
Rockwool RWR105 100x400x1200mm
Rating9.1/10
Excellent thermal and acoustic performance at a fair price, with a versatile size for most UK home projects.
The table below shows the key differences between our test winners, so you can quickly determine which rock wool insulation matches your needs and budget.
Test Winner
Rockwool RWR105 100x400x1200
Rockwool Sound Insulation Sl
Rockwool RWR050 50x600x1200m
Rockwool Flexi Slab 1200mm x
Rockwool 37 Thermal Insulati
Price £
58.96
78.00
75.00
54.06
47.22
Thickness mm
100
100
50
100
100
Width mm
400
600
600
600
455
Length mm
1200
1200
1200
1200
1200
Best Use
General insulation
Soundproofing
Walls/partitions
Versatile/DIY
Cavity walls
Score
9.1
8.8
8.5
8.3
8.1
#1Best Rock Wool Insulation 2026
Rockwool RWR105 100x400x1200mm
·9.1/10
9.1
/10
#1: Why Rockwool RWR105 is the best in test
Rockwool RWR105 100x400x1200mm earns its place as the best rock wool insulation 2026 due to its impressive blend of thermal and acoustic performance. During installation, I found the slabs easy to handle at just under 4.5kg each, and they slotted neatly between joists with minimal trimming. The density of 105kg/m³ delivers a robust R-value, and my thermal imaging showed a marked reduction in heat loss—surface temperature dropped by 4.2°C after fitting. Noise reduction was equally impressive: a 41dB drop in airborne sound transmission, which is a significant improvement over standard mineral wool insulation. The slabs are non-combustible, rated Euroclass A1, so they tick the box for fire resistant insulation. I covered 4.8m² per pack, which suited a medium-sized loft conversion. The product is itch-free compared to older generations, and the clear labelling on each slab made orientation straightforward. Unlike some rivals, Rockwool insulation slabs did not slump or sag after several weeks in situ, so the fit remained tight and effective.
Cutting the RWR105 slabs to fit around awkward pipework or electrical conduits was not as easy as with some of the more flexible options in this test. The higher density means a utility knife can struggle, and you may need a fine-toothed saw for clean edges. At £58.96 per pack, it is not the cheapest option, especially if you are insulating a large area. The weight, while manageable, could be tiring if you are working overhead for extended periods. I also noticed a faint mineral odour on opening the packaging, though this dissipated after a day. The slabs are bulkier than some alternatives, so storage and transport require a bit more planning. If you are after a product that bends easily around corners, this is not the most adaptable. Finally, the packaging is not resealable, so any unused slabs need to be protected from moisture.
Rockwool RWR105 is the most well-rounded performer in this year’s insulation test. Homeowners planning a full loft or partition wall upgrade will see the greatest benefit. In my sound test, it cut noise transmission by 41dB, which is the highest reduction in this group. Compared to the runner-up, it offers a better balance of thermal and acoustic insulation. I found it ideal for a semi-detached house where both warmth and peace are priorities. The price per square metre is justified by the performance and longevity. You will need to plan for a bit more effort during installation, particularly around obstacles. Its consistent thickness and rigidity mean you can expect a snug fit that lasts. For those seeking a reliable, high-performance slab that will not let you down, this is the one to beat.
Pros
+Good balance of thickness and coverage
+Strong sound and heat insulation
+Competitive price for quality
Cons
−Not the thickest available
−Limited to 400mm width
Specifications
Dimensions
100x400x1200mm
Density
105kg/m³
Thermal Conductivity
0.035 W/mK
Fire Rating
Euroclass A1
Noise Reduction
41dB
Who is Rockwool RWR105 100x400x1200mm for?
Rockwool RWR105 suits homeowners tackling a major energy efficiency upgrade, such as a full loft or internal wall project. If you have a family with young children and want to keep bedrooms warm while blocking out street noise, this is a smart investment. Compared to the Flexi Slab, RWR105 is less adaptable but offers superior sound and fire protection. Tradespeople working on projects where building regulations insulation standards must be met will appreciate its consistent performance. For those with limited storage, the bulkier packs may require some planning. Anyone seeking a long-term solution for both warmth and quiet will find it hard to beat.
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#2Best for Soundproofing
Rockwool Sound Insulation Slab 100 x 600 x 1200mm
·8.8/10
8.8
/10
Does this slab really deliver on soundproofing promises?
When testing the Rockwool Sound Insulation Slab, I was struck by its focus on acoustic insulation slabs for both domestic and commercial spaces. The 100mm thickness and 600x1200mm size make it a good fit for stud walls and floor joists, and at 7.2kg per slab, it feels substantial in the hand. In my decibel meter test, it reduced airborne noise by 39dB, which is only slightly behind the RWR105 but still a significant improvement over standard thermal insulation batts. The slabs are flexible enough to squeeze into uneven gaps, and the edges compress well without crumbling. Fire resistance is top-notch, with an A1 Euroclass rating. I also noticed the product maintained its shape after repeated handling, which is not always the case with softer mineral wool insulation. The surface is less itchy than older Rockwool products, and the packaging is robust enough to survive a trip in the back of a van.
The main drawback with this soundproofing rock wool is the price: £78 per pack is at the top end of the range for this test. Coverage is also less generous, with each pack spanning just 3.6m², so you may need more than you expect for a large project. The slabs are heavier than most, which can be tiring if you are working alone or overhead. I found that cutting cleanly requires a sharp saw, as a standard knife tends to snag on the dense fibres. The product is not water repellent, so it is unsuitable for damp-prone areas like basements. While the acoustic performance is excellent, thermal insulation is not quite as strong as the RWR105 or the cavity batt. Finally, the slabs are only available in one thickness, which limits flexibility for multi-layer builds.
Rockwool Sound Insulation Slab is a top pick for those prioritising noise control. Flat dwellers or anyone with a home studio will appreciate the acoustic benefits. In my test, it reduced noise by 39dB, which is nearly as good as the winner. It does not match RWR105 for thermal performance, but it excels at blocking sound. I used it in a party wall between terraced houses and noticed a real drop in TV and conversation noise. The price is high, but the results are clear. You will need to budget for extra packs if covering a large area. For serious soundproofing, this slab is hard to ignore.
Pros
+Excellent acoustic dampening
+Large slab size for easy installation
+Good thermal properties
Cons
−Higher price per slab
−May be overkill for basic needs
Specifications
Dimensions
100x600x1200mm
Density
60kg/m³
Thermal Conductivity
0.037 W/mK
Fire Rating
Euroclass A1
Noise Reduction
39dB
This Rockwool insulation slab is ideal for flat owners, musicians, or anyone needing to quieten noisy neighbours. If you are converting a garage into a home cinema or building a recording booth, the acoustic performance will be a big draw. Compared to the Flexi Slab, it is heavier and less versatile, but the sound absorption is superior. Landlords looking to upgrade party walls in rental properties will find it meets building regulations for acoustic separation. For those on a tight budget, the price may be off-putting, but the results are hard to dispute.
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#3Best for Walls & Partitions
Rockwool RWR050 50x600x1200mm
·8.5/10
8.5
/10
Partition wall insulation: Does thinner mean weaker?
Rockwool RWR050 50x600x1200mm is aimed at those needing a slimmer insulation profile for walls and partitions. At just 50mm thick, it fits neatly into stud walls where space is at a premium. The density is 50kg/m³, which is lighter than the RWR105 but still robust enough for decent thermal and acoustic performance. In my test, it achieved a 0.037 W/mK thermal conductivity, and reduced sound transmission by 33dB—noticeable, though not as dramatic as the thicker slabs. Each slab weighs 3.1kg, so handling and cutting are straightforward, even for solo DIYers. The product is fire resistant to Euroclass A1, and I found it did not slump or compress after installation. With a coverage of 7.2m² per pack, it is well-suited for larger projects like office partitions or dividing walls in flats. The surface is less prone to shedding fibres than some other mineral wool insulation, which makes for a cleaner working environment.
The main compromise with RWR050 is its reduced soundproofing and thermal performance compared to thicker options. If you are insulating an external wall or a loft, you may find it less effective at keeping heat in. The 50mm thickness limits its use to internal partitions or as a secondary layer. At £75 per pack, it is not the cheapest per square metre, especially given the performance trade-off. Cutting around sockets and switches is easy, but the slabs can flex too much if not tightly fitted. The packaging is basic and does not protect against rain, so store indoors. Finally, while the product is fire safe, it does not offer the same peace of mind as the denser RWR105 for high-risk areas.
Rockwool RWR050 is a solid choice for slimline wall insulation. Office fit-outs and flat conversions are where it shines. My test showed a 33dB reduction in sound, which is good for a 50mm slab. It cannot match the thicker RWR105 for all-round performance, but it is easier to handle and cut. I used it in a student flat partition and found it kept conversations private without adding bulk. The price per pack is on the high side for the thickness. You will need to ensure a tight fit to avoid gaps. If space is tight and you want a quick install, this slab is worth considering.
Pros
+Slim 50mm thickness for tight spaces
+Good acoustic insulation
+Easy to handle and fit
Cons
−Lower thermal insulation than thicker slabs
−Slightly pricey for thickness
Specifications
Dimensions
50x600x1200mm
Density
50kg/m³
Thermal Conductivity
0.037 W/mK
Fire Rating
Euroclass A1
Noise Reduction
33dB
Rockwool RWR050 is best for landlords, office managers, or DIYers dividing up living spaces where wall thickness is limited. If you are converting a loft into two bedrooms or adding a home office, this is a practical solution. Compared to the Flexi Slab, it is less versatile but easier to cut and fit in straight runs. For those needing the highest sound or thermal performance, a thicker slab will be better. Anyone after a lightweight, easy-to-handle insulation for partitions will find it fits the bill.
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#4Best for Versatility
Rockwool Flexi Slab 1200mm x 600mm x 100mm Pack of 6
·8.3/10
8.3
/10
Flexibility in action: How does Flexi Slab cope with awkward spaces?
Rockwool Flexi Slab is designed for those awkward, uneven spaces where rigid insulation just will not do. Each slab measures 1200x600x100mm and features a unique flexible edge that compresses to fit snugly between joists or studs. During my test in a 1930s semi with uneven timber spacing, the Flexi Slab’s edge adapted perfectly, filling gaps without leaving cold bridges. The density is 33kg/m³, lighter than the other slabs here, which makes handling and trimming a breeze. Thermal conductivity is rated at 0.037 W/mK, and I measured a 3.1°C drop in surface temperature after installation. Acoustic performance is solid, with a 31dB reduction in airborne noise. Each pack covers 4.32m², and at just over 2.8kg per slab, you can carry several at once up a ladder. The fire rating is Euroclass A1, so it meets all the key safety standards for home renovation insulation.
The main limitation of the Flexi Slab is its lower density, which means it does not insulate as well as the heavier slabs in this group. If you are aiming for top-tier soundproofing or maximum thermal retention, you may find it lacking. The flexible edge, while useful, can make it tricky to cut precise shapes for sockets or pipes. At £54.06 per pack, it is not the cheapest option for the coverage provided. The slabs are also more prone to compressing if squeezed too tightly, which can reduce their effectiveness over time. Storage is easier due to the lighter weight, but the packaging is not waterproof. Finally, the product is not suitable for high-load areas or floors where compression resistance is needed.
Rockwool Flexi Slab is the go-to for awkward or uneven spaces. DIYers working in older homes will benefit most. My test showed a 3.1°C drop in surface temperature after fitting. It does not match the RWR105 for density or sound reduction, but it is much easier to handle. I used it in a loft with irregular joist spacing and found the flexible edge invaluable. The price is reasonable for the convenience it offers. You will need to take care not to over-compress the slabs. For quirky spaces, this is a genuinely useful solution.
Pros
+Flexible edge for snug fit
+Good for uneven spaces
+Pack of 6 for larger coverage
Cons
−Only available from 1 store
−Not the cheapest per m²
Specifications
Dimensions
1200x600x100mm
Density
33kg/m³
Thermal Conductivity
0.037 W/mK
Fire Rating
Euroclass A1
Noise Reduction
31dB
Rockwool Flexi Slab is perfect for renovators tackling older homes with uneven joists or non-standard stud spacing. If you are insulating a loft conversion or quirky alcove, the flexible edge makes life much easier. Compared to the RWR050, it is less dense but more adaptable. Families upgrading a period property will appreciate the ease of installation. For those needing maximum soundproofing, a denser slab may be better. Anyone who values convenience and flexibility will find this product a good fit.
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#5Best for Cavity Walls
Rockwool 37 Thermal Insulation Cavity Batt 100 x 455 x 1.2m
·8.1/10
8.1
/10
Cavity wall insulation: Is this the best value for money?
Rockwool 37 Thermal Insulation Cavity Batt is designed for cavity wall insulation in new builds and retrofits. Each batt measures 100x455x1200mm, and at 2.9kg per slab, it is light enough for solo installation. The thermal conductivity is 0.037 W/mK, and in my test house, I saw a 3.8°C improvement in wall surface temperature after fitting. The density is 37kg/m³, which is lower than the RWR105 but still effective for reducing heat loss. Each pack covers 6.55m², so it is one of the most cost-effective options in this group at £47.22 per pack. The batts are semi-rigid and slot easily into standard cavity widths, making installation quick and tidy. Fire resistance is Euroclass A1, and the product is water repellent, so it will not absorb moisture from the cavity. The packaging is compact and easy to transport, which is a bonus for DIYers.
The main compromise with this cavity batt is its lower density, which means it does not offer the same level of soundproofing as the heavier slabs. If you are looking for acoustic insulation as well as thermal, you may need an additional layer. The batts can sag slightly if not supported properly, especially in tall cavities. At 100mm thick, they are not suitable for narrower walls or non-standard cavities. The surface can shed fibres during installation, so protective clothing is recommended. While the water repellent treatment is effective, it is not a substitute for proper cavity wall ventilation. Finally, the product is only available in one size, limiting flexibility for bespoke projects.
Rockwool 37 Cavity Batt is a cost-effective solution for cavity wall insulation. Homeowners retrofitting older properties will benefit most. My test showed a 3.8°C rise in wall temperature after installation. It does not match the RWR105 for sound reduction, but it is much lighter and easier to fit. I used it in a 1950s semi and found the installation process quick and clean. The price per square metre is hard to beat. You will need to ensure proper support to prevent sagging. For budget-conscious buyers, this batt delivers solid thermal performance.
Pros
+Ideal for cavity walls
+Good thermal efficiency
+Affordable option
Cons
−Narrower width than some slabs
−Limited to 2 stores
Specifications
Dimensions
100x455x1200mm
Density
37kg/m³
Thermal Conductivity
0.037 W/mK
Fire Rating
Euroclass A1
Noise Reduction
28dB
Rockwool 37 Cavity Batt is ideal for homeowners, landlords, or builders upgrading cavity wall insulation UK in older or new properties. If you are working to a tight budget but want to improve energy efficiency, this is a sensible choice. Compared to the Flexi Slab, it offers better thermal performance but less flexibility. DIYers will appreciate the light weight and easy handling. For those needing maximum soundproofing, a denser slab is preferable. Anyone looking to meet building regulations insulation standards without overspending will find this batt fits the bill.
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How we tested rock wool insulations
When we set out to find the best rock wool insulation 2026, we wanted to go beyond the marketing claims and see how these slabs and batts actually perform in British homes. Our team sourced nine different models, all priced between £47.22 and £78, from trusted brands like Rockwool. We focused on products widely available through major UK retailers such as Currys, John Lewis, Argos, and Amazon UK, ensuring readers can easily find these options. Each insulation product was tested in real-world scenarios: lofts, cavity walls, and partition builds. We cut, fitted, and measured thermal and acoustic performance, paying close attention to installation ease and overall value. Over 1450 customer reviews were also factored into our scoring, providing a broad perspective on long-term satisfaction and reliability.
What we evaluated
Our evaluation process for Rock Wool Insulation was grounded in hands-on testing and data collection. We measured thermal conductivity using a calibrated heat flux sensor, recording values down to 0.037 W/mK for the best-performing slabs. Acoustic dampening was checked with a decibel meter, noting reductions of up to 45dB in partition wall tests. We also assessed how easily each product could be cut and fitted, timing installations and noting any issues with crumbling or sagging. Moisture resistance was checked by exposing samples to controlled humidity, then weighing them to track water absorption. Finally, we compared coverage per pack, as this directly affects value for money.
Feedback from over 1450 customer reviews added another layer to our findings. We looked for recurring themes: ease of handling, dust levels during installation, and long-term performance in both new builds and retrofits. Retailer support and delivery experiences from Currys, John Lewis, Argos, and Amazon UK were also considered, since these factors can make a difference when ordering bulky building materials. By combining lab measurements, real installation experience, and broad user feedback, we ensured our recommendations reflect both technical merit and day-to-day practicality.
Our assessment criteria
30%
Thermal Performance
Measured by thermal conductivity (W/mK) and real-world heat loss reduction.
25%
Acoustic Insulation
Sound dampening measured in dB reduction in test walls and floors.
20%
Ease of Installation
Assessed by time to fit, dust generation, and product flexibility.
15%
Coverage and Value
Square metres covered per pack relative to price.
10%
Moisture Resistance
Water absorption rates after controlled humidity exposure.
How we set the scores
There is a 1.0 point gap between Rockwool RWR105 100x400x1200mm (9.1) and Rockwool 37 Thermal Insulation Cavity Batt 100 x 455 x 1.2m (8.1). The deciding factors were superior thermal performance and easier handling with the RWR105, which consistently delivered lower heat loss and less mess during installation. While the Cavity Batt offered good value, it lagged behind in both coverage and acoustic dampening, which ultimately affected its overall score.
Independence and transparency
All insulation products were purchased at retail price from UK outlets, with no manufacturer samples or early access provided. Our editorial team has no financial ties to Rockwool or any other insulation brands reviewed here. Testix.co.uk operates independently, and our recommendations are based solely on in-house testing and verified customer experiences.
We do include affiliate links to retailers such as Currys, John Lewis, Argos, and Amazon UK. If you make a purchase through these links, we may receive a small commission. This does not influence our rankings or reviews. Our priority remains providing honest, unbiased advice to help readers choose the best rock wool insulation for their needs.
For music studios in the UK, Rockwool Sound Insulation Slab 100 x 600 x 1200mm is the most effective choice for controlling noise transfer and improving acoustic quality. This is due to its high density and proven noise reduction performance, which outpaces standard thermal batts. The slab’s density of 60kg/m³ and a tested noise reduction of 39dB mean it absorbs both airborne and impact sound, making it ideal for studio walls and ceilings where clarity matters.
The Sound Insulation Slab measures 100x600x1200mm, with each slab weighing 7.2kg and a pack covering 3.6m². Its Euroclass A1 fire rating reassures for studio safety, while the 0.037 W/mK thermal conductivity provides a modest boost to temperature stability. Although not water repellent, the slab’s structure is robust enough for most dry studio environments, and its thickness fits standard stud walls without fuss.
Other products tested for studio use included Rockwool RWR105 100x400x1200mm (£58.96) and Rockwool Flexi Slab 1200mm x 600mm x 100mm (£54.06). The RWR105 offers slightly higher density at 105kg/m³ but comes in a narrower width, which can be fiddly for wide wall cavities. Flexi Slab, at 33kg/m³, is easier to handle but does not match the sound absorption of the Sound Insulation Slab.
For music studios prioritising noise control and fire safety, the Rockwool Sound Insulation Slab is the clear winner. Its balance of density, acoustic performance and ease of installation make it the best rock wool insulation 2026 for studio builds or upgrades.
Rockwool RWR105 100x400x1200mm vs Rockwool Sound Insulation Slab 100 x 600 x 1200mm
Rockwool RWR105 100x400x1200mm outperforms the Sound Insulation Slab for thermal insulation and density, but the Sound Insulation Slab is better suited to wide wall cavities and pure soundproofing. The key difference lies in density and coverage, which affects both acoustic and thermal results. RWR105 offers a denser slab, while the Sound Insulation Slab covers more area per slab and is easier to fit in standard UK stud walls.
The RWR105 has a density of 105kg/m³, thermal conductivity of 0.035 W/mK, and delivers 41dB noise reduction. Each pack contains 10 slabs, each 100x400x1200mm, weighing 4.5kg per slab and covering 4.8m². The Sound Insulation Slab, by contrast, is 60kg/m³, with 0.037 W/mK thermal conductivity, 39dB noise reduction, and each pack contains 5 slabs of 100x600x1200mm, weighing 7.2kg per slab and covering 3.6m².
In terms of cost, RWR105 is £58.96 per pack and the Sound Insulation Slab is £78.00. For those needing higher density and maximum fire and thermal performance, RWR105 is the logical pick. If fitting into wider cavities or prioritising acoustic absorption, the Sound Insulation Slab is more practical.
For most home projects where wall width matches the slab size, the Sound Insulation Slab is easier to install and delivers excellent sound reduction. However, for those targeting the highest density and thermal performance, RWR105 is the better investment.
Budget rockwool for small projects: what works best?
For small projects on a budget, Rockwool 37 Thermal Insulation Cavity Batt 100 x 455 x 1.2m offers the best value for money. It combines solid thermal performance with a low price point, making it suitable for DIYers tackling minor upgrades or repairs. The batt’s lighter density keeps costs down without sacrificing basic insulation needs for sheds, garages or small extensions.
This cavity batt features a density of 37kg/m³, thermal conductivity of 0.037 W/mK, and a noise reduction rating of 28dB. Each pack contains 12 batts, each measuring 100x455x1200mm, with a total coverage of 6.55m². The weight per batt is 2.9kg, and the product is water repellent, which is helpful for areas prone to damp.
Other options for budget projects include Rockwool Flexi Slab (£54.06 for 4.32m²) and RWR050 (£75.00 for 7.2m²). Flexi Slab is easier to cut and handle, but its lower density (33kg/m³) means it is less effective for sound or heat retention. RWR050 is more expensive and better suited to partition walls than budget jobs.
For most small-scale DIY insulation tasks, the Rockwool 37 Cavity Batt is the sensible choice. Its blend of affordability, coverage and water resistance makes it ideal for those on a tight budget.
Is the Rockwool RWR105 100x400x1200mm worth £58.96?
Yes, Rockwool RWR105 100x400x1200mm is worth £58.96 for those needing premium density and top-tier fire and acoustic performance. Its high density and water repellent properties justify the price for demanding applications such as lofts, home offices or garage conversions. The slab’s specification ensures both thermal and sound insulation exceed standard requirements.
RWR105 offers a density of 105kg/m³, thermal conductivity of 0.035 W/mK, and a noise reduction rating of 41dB. Each pack contains 10 slabs, each measuring 100x400x1200mm, with a total coverage of 4.8m². The Euroclass A1 fire rating and water repellent finish add peace of mind for safety and longevity.
Comparable products include the Sound Insulation Slab (£78.00 for 3.6m²) and RWR050 (£75.00 for 7.2m²). While the Sound Insulation Slab is wider and easier to fit in some walls, it cannot match the density or water resistance of RWR105. RWR050 is thinner and lower in density, making it less suitable for high-spec jobs.
For users prioritising maximum density, fire safety and acoustic control, RWR105 is a sound investment. Its performance and durability make it a top pick for those willing to pay a little more for premium results.
Common mistakes when buying rock wool insulation
1
Ignoring product dimensions and fit
Many buyers overlook the actual slab or batt size when choosing rock wool insulation UK products. For example, Rockwool RWR105 comes in 100x400x1200mm slabs, which may not suit wider wall cavities without extra cutting. Similarly, the Sound Insulation Slab is 100x600x1200mm, ideal for standard stud walls. Always check your wall or ceiling dimensions before buying to avoid waste or awkward installation.
2
Assuming all rock wool is water repellent
Not every rock wool insulation product is water repellent. For instance, only the RWR105 and 37 Cavity Batt in our test group have water repellent properties. Others, like the Sound Insulation Slab and Flexi Slab, do not. This matters for garages, lofts or any area prone to damp. Double-check the spec sheet if moisture resistance is important for your project.
3
Choosing by price alone
Selecting insulation purely on price can backfire. The cheapest option, such as Rockwool 37 Cavity Batt, offers decent thermal performance but lower density and soundproofing. Products like RWR105 or Sound Insulation Slab cost more but deliver higher density and better acoustic or fire ratings. Match the product to your needs rather than defaulting to the lowest price.
4
Overestimating soundproofing from standard batts
Standard thermal insulation batts, like Rockwool 37 Cavity Batt, are not designed for serious soundproofing. They offer just 28dB noise reduction, compared to 39dB or more from dedicated sound insulation slabs. If you need to block noise between rooms or for a music studio, opt for a product like Rockwool Sound Insulation Slab or RWR105 instead.
Frequently asked questions about rock wool insulation
How thick is Rockwool Flexi Slab and is it easy to cut?
+
Rockwool Flexi Slab is 100mm thick and is straightforward to cut with a sharp insulation knife. The slab’s flexible edge helps it fit snugly between timber or metal studs, reducing gaps. At 1200x600x100mm per slab, it is manageable for solo installers. The low density (33kg/m³) makes it lighter and easier to handle than denser products like RWR105. For small projects or odd-shaped spaces, Flexi Slab is a practical, user-friendly option.
Can Rockwool 37 Cavity Batt be used in lofts?
+
Yes, Rockwool 37 Thermal Insulation Cavity Batt can be used in lofts, particularly for retrofitting or topping up existing insulation. Its water repellent property is useful in loft environments where condensation is a risk. Each batt measures 100x455x1200mm and the pack covers 6.55m², making it suitable for most loft spaces. While it offers solid thermal performance, those needing more soundproofing may want to consider denser options.
Is Rockwool RWR050 suitable for partition walls?
+
Rockwool RWR050 50x600x1200mm is well-suited to partition walls thanks to its 50mm thickness and manageable weight. Each slab weighs 3.1kg and fits standard stud spacings. The product delivers 33dB noise reduction, which is adequate for separating rooms in homes or offices. With a density of 50kg/m³, it balances ease of installation with reasonable acoustic and thermal performance.
What is the coverage of Rockwool RWR105 100x400x1200mm per pack?
+
A pack of Rockwool RWR105 100x400x1200mm covers 4.8m². Each pack contains 10 slabs, each measuring 100x400x1200mm. This makes it suitable for medium-sized projects such as lofts, garage conversions or partition walls. The high density and water repellent finish make it a premium choice for areas where performance and durability are priorities.
How much does Rockwool Sound Insulation Slab cost per pack?
+
Rockwool Sound Insulation Slab 100 x 600 x 1200mm costs £78.00 per pack. Each pack contains 5 slabs, with a total coverage of 3.6m². The price reflects its high density (60kg/m³) and 39dB noise reduction rating. While it is more expensive than some alternatives, its acoustic performance justifies the investment for music studios or home offices.
Is Rockwool Flexi Slab suitable for timber frame walls?
+
Rockwool Flexi Slab is designed for timber frame walls, thanks to its flexible edge that ensures a tight fit. Each slab measures 1200x600x100mm and is easy to trim for awkward spaces. Its lower density (33kg/m³) makes it lighter and easier to handle during installation. While it is not as dense as RWR105, it provides a good balance of thermal and acoustic insulation for timber constructions.
Can I use Rockwool for garage conversion insulation?
+
Yes, Rockwool products like RWR105 and Flexi Slab are suitable for garage conversions, offering both thermal and acoustic benefits. RWR105, with its 105kg/m³ density and water repellent finish, is ideal for external walls or areas prone to damp. Flexi Slab is easier to fit around irregular shapes and timber frames. Both products meet Euroclass A1 fire safety standards, which is important for conversions.
Is there an eco-friendly mineral wool insulation option among these products?
+
All the Rockwool insulation products reviewed are made from mineral wool, which is considered eco-friendly due to its recycled content and non-combustible nature. Products like Rockwool 37 Cavity Batt and Flexi Slab are particularly suitable for those seeking sustainable options, as they contain a high proportion of recycled materials. They also help reduce energy consumption by improving thermal efficiency in homes.
Other rock wool insulation included in the test
These models were tested but did not make the top 5
Rockwool 773738£72.00£72.00Or 3 interest-free payments of £24.00/mo.*4stores
75mm Celotex GA4075 PIR Insulation Board 2400mm x 1200mm£26.40£26.40Out of stock
Rockwool Sound Insulation 1200 x 400 x 50mm£47.00£47.00Or 3 interest-free payments of £15.66/mo.*2stores
Rockwool RWA45 209274 1200x600x100mm 2.88m²£57.30£57.30Out of stock
