Choosing what to put inside a wall cavity can be confusing because thermal insulation, acoustic mineral wool, plasterboard and dense soundproofing boards all perform different jobs. A product can be excellent thermal insulation without being the best choice for acoustic cavity absorption.
For most internal soundproofing walls, the cavity layer is chosen to reduce resonance and absorb sound energy within the void. The mass and decoupling are then provided by other parts of the wall system.
Best cavity insulation for soundproofing
For an internal stud or independent wall lining, acoustic mineral wool is normally the first material to consider. Soundproofing King stocks several suitable options:
- Rockwool RWA45 – 45kg/m³ stone wool available for a wide range of wall and ceiling applications.
- Rockwool RW3 – a denser stone-wool slab for suitable acoustic constructions.
- Knauf APR Acoustic Roll – glass-mineral-wool acoustic partition roll.
- ISOVER APR 1200 – another acoustic partition roll for suitable internal partitions.
Choose a thickness that fits the available cavity without excessive compression. An air-filled or poorly treated cavity can resonate; a correctly fitted porous infill helps control that energy.
What about PIR cavity boards?
Products such as Soprema Sopratherm CW4000 are primarily thermal cavity insulation. PIR can be the right choice when thermal performance is the main requirement, but it should not automatically be substituted for acoustic mineral wool in an internal soundproofing wall.
That distinction is important. PIR is rigid, closed-cell thermal insulation; acoustic mineral wool is porous and is used to absorb sound energy within cavities. If a project requires both acoustic and thermal performance, the whole construction needs to be designed around both requirements rather than assuming one product does every job.
What about moisture-resistant plasterboard?
Siniat GTEC Moisture Board is chosen primarily where moisture resistance is required. It is a lining board, not the cavity infill. In bathrooms, kitchens or other higher-humidity spaces it may form part of the finished wall system, but the cavity still needs to be specified separately.
What about acoustic plasterboard?
Dense acoustic plasterboards add mass to the wall face. Options include Siniat GTEC dB Board and Gyproc SoundBloc. These are useful lining layers but do not replace the mineral wool inside the cavity.
For still more mass in a suitable build-up, consider SPK15 Sand Board or a flexible acoustic membrane/MLV layer.
How the layers work together
A soundproof wall is usually more effective when each layer has a clear job:
| Layer | Main acoustic job | Examples |
|---|---|---|
| Cavity infill | Absorb sound energy and reduce cavity resonance | RWA45, RW3, Knauf APR, ISOVER APR |
| Decoupling | Reduce direct vibration transfer | GenieClip RST and furring channel |
| Mass | Resist airborne sound transmission | SoundBloc, Siniat dB, SPK15, MLV, Tecsound |
| Sealing | Close weak air paths | AC50 acoustic sealant |
Should the cavity be completely packed?
Follow the chosen wall-system guidance. Do not assume that forcing the thickest possible mineral wool into the cavity is better. Heavy compression changes the way the material sits in the void and can make installation difficult. Match the insulation thickness to the cavity depth and keep coverage neat and continuous.
What if you are building against an existing masonry wall?
For a noisy party wall, the new cavity may sit within an independent lining or a decoupled clip system. Read our concrete and masonry wall soundproofing guide and browse the wall soundproofing collection.
Common mistakes
- Using PIR as a direct substitute for acoustic mineral wool because both products are called insulation.
- Assuming moisture-resistant plasterboard is a specialist soundproofing board.
- Leaving large gaps in the cavity insulation.
- Compressing an oversized insulation product into a shallow cavity.
- Ignoring mass and decoupling and expecting cavity insulation alone to stop neighbour noise.
- Failing to seal the wall perimeter and penetrations.
Recommended wall-cavity products
Start with our acoustic mineral wool collection. For a complete wall build, combine the correct cavity product with clips and channels, acoustic plasterboard, membranes where required and AC50 acoustic sealant.
If you send us the stud depth, wall dimensions and noise problem, Soundproofing King can help you choose the right cavity fill and lining products.
