At a glance
Impact noise from upstairs rooms is the single most common sound complaint in UK homes, ahead of even neighbour noise through party walls. Footsteps, dropped items, chairs scraping and children running are all examples of impact noise, and a timber-joist ceiling with nothing in the voids transmits every one of those impacts directly to the room below with almost no attenuation. The right ceiling insulation turns this from a daily irritation into a background murmur.
Acoustic ceiling insulation works on two different types of sound: airborne (voices, TV, music) and impact (footsteps, objects hitting the floor above). Different products handle these two categories with different efficiency, and the best choice depends on which problem dominates in your home. We tested six of the most popular products available in the UK, with performance assessed by a combination of manufacturer acoustic data, real-world fit characteristics and installer feedback from trade users across the country.
How ceiling acoustic insulation actually works
Sound travels through a ceiling via three paths: airborne waves that vibrate the plasterboard, impact vibration transmitted through the joists, and flanking transmission around the edges via walls and gaps. Insulation fitted into the void between joists addresses primarily the airborne path by absorbing sound energy within the material’s fibres. Dense mineral wool products also dampen joist vibration to a small degree by adding mass to the system. For serious impact noise reduction, insulation alone is only half the answer – the other half is resilient mounting of the plasterboard below, typically using acoustic hangers or resilient bars.
The key specification to look for is density. Acoustic performance broadly correlates with product density – heavier products (60kg/m³ and above) outperform lighter thermal-first products (10-15kg/m³) significantly for airborne noise. Impact noise reduction is far more dependent on the ceiling system as a whole than on the insulation alone. For a typical UK home with timber joists and standard 12.5mm plasterboard, adding 100mm of dense mineral wool typically reduces airborne sound transmission by 10-15 decibels, which is a substantial and immediately noticeable improvement.
All 6 products ranked
Density of 45kg/m³ puts the RWA45 firmly in acoustic-grade territory and the performance shows it. Sound absorption coefficient of 1.0 across the critical 500Hz-2kHz range means it traps essentially all the airborne sound energy passing through it. Non-combustible A1 fire rating is an added benefit for ceiling applications where any fire risk is a serious concern.
The trade-off is handling – at 45kg/m³ the slabs are heavy and the fibres require respiratory protection during fitting. For a ceiling install this is manageable but not pleasant. Priced in the middle of the test range but delivers premium acoustic performance.
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The Flexi slab uses a flexible spring-back edge that allows it to be cut slightly oversized and wedged firmly between joists without any mechanical fixings. For a ceiling install this is genuinely useful – gravity works against you with rigid slabs and Flexi’s self-retention cuts installation time significantly. Acoustic performance at 30-40kg/m³ is slightly below the RWA45 but still firmly in the acoustic-grade category.
Best choice for DIY installs where a working-from-below approach matters. Slightly more expensive per m² than the RWA45 but the time saving often justifies it for one-person installs.
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Supplied as a rolled product rather than slabs, the Isover APR is faster to cut and fit in ceilings with consistent joist spacing. Density sits at 11-16kg/m³ which is lower than the Rockwool options – acoustic performance is still respectable for airborne sound but noticeably less effective on lower frequency impact noise.
Cost per m² is among the lowest in the test, making it attractive for large-area installs where budget is the main constraint. Good for airborne sound reduction in typical domestic applications but not the first choice where impact noise is the primary complaint.
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Knauf’s Earthwool Acoustic sits at the sweet spot of cost and performance for most UK domestic ceiling projects. Density of around 10-16kg/m³ matches the Isover product but the bio-soluble glass wool fibres are less irritating to handle, which matters on an overhead install. Thermal benefit is a useful secondary – this is a genuine dual-purpose insulation.
The lowest price per m² in the test and widely available from trade merchants and DIY stores. For the budget-conscious homeowner looking to address general upstairs noise, this is an easy recommendation.
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The highest density product in the test at 60kg/m³. Sold under various white-label names in the UK (often labelled as “acoustic mineral wool slab 60kg”) this is the performance ceiling for domestic ceiling insulation. Used in commercial studio builds and high-end domestic refurbs where noise reduction is the primary goal regardless of cost.
Fit is challenging due to weight and slab rigidity. Best installed during a renovation while the ceiling is open. Overkill for general domestic noise reduction but unmatched when every decibel counts.
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PIR rigid foam insulation like the Celotex GA4000 is primarily designed for thermal performance, not acoustic. Acoustic performance is substantially lower than any of the mineral wool options in this test because the closed-cell rigid structure does not absorb sound energy effectively. Included here because PIR products are frequently purchased for ceiling applications by buyers confused about the difference.
Useful only if you need thermal insulation and acoustic is a nice-to-have secondary benefit. For a genuine acoustic install this is the wrong material regardless of price.
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Specification comparison
Installation approach for best results
Installing acoustic insulation in a ceiling void is straightforward in principle but the details matter significantly for the final acoustic performance. Below is the step-by-step approach that delivers consistent results regardless of which product you choose.
Measure joist spacing accurately
Most UK ceilings have joists at 400mm or 600mm centres. Measure rather than assume – older houses often have inconsistent spacing. Cut your slabs or roll 10-15mm oversized for a friction fit.
Wear full PPE
Mineral wool fibres are skin and respiratory irritants. Overhead work means fibres fall directly onto you. Long sleeves, gloves, safety goggles and an FFP3 dust mask are non-negotiable.
Fill the full depth of the joist void
Partial filling dramatically reduces acoustic performance. Fit insulation to the full joist depth with no gaps at the top or sides. Two layers stacked is better than one partial layer with an air gap above.
Consider resilient bars for impact noise
For serious impact noise reduction, resilient bars (acoustic hangers) between joists and plasterboard are as important as the insulation. They decouple the ceiling surface from the joists, stopping impact vibration cold.
Seal edges and penetrations
Acoustic mastic around the perimeter of the new plasterboard and around light fittings, cable runs and pipes prevents flanking transmission. A single 3mm gap around a ceiling rose can halve the effective sound reduction of the whole install.
Check for downlighters before cutting insulation. Standard low voltage halogen or LED downlighters must not be covered with insulation unless they are fire-rated and insulation-compatible (marked IC rated or similar). Direct contact with flammable insulation around older fittings creates a genuine fire risk. For modern installs, use IC-rated covers or hoods around the light fittings before fitting insulation over the top.
Which product to choose
For most UK homes wanting to meaningfully reduce upstairs noise, the Rockwool RWA45 is the right choice. It delivers strong acoustic performance, is widely available, fire-rated A1 and sits at a reasonable price point. It handles airborne sound exceptionally well and is perfectly adequate for impact noise when combined with a proper installation.
For DIY installs working from below, the Rockwool Flexi is the practical choice. The self-retention feature dramatically simplifies ceiling fitting and the acoustic performance is very close to the RWA45 for most frequencies of interest. For extensive installs the cost difference is offset by the time saving.
For budget-conscious homeowners, the Knauf Earthwool represents the best value at around £20 per m². Performance is measurably lower than the Rockwool products but for general domestic noise complaints it makes an immediate noticeable difference and works out at roughly half the installed cost.
For professional studio or media-room builds where every decibel matters, the 60kg mineral wool slab is the tool of choice. Overkill for general domestic use but unmatched when the goal is serious acoustic isolation.
Density is the single most important factor in ceiling acoustic performance, and the Rockwool RWA45 at 45kg/m³ hits the sweet spot of performance and practicality for UK homes. Avoid PIR products for acoustic applications – they are designed for thermal work and the acoustic performance is a long way behind mineral wool alternatives.
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