Rockwool RW3 25mm

ROCKWOOL RW3 25mm Technical Specifications

ROCKWOOL RW3 25mm Acoustic Mineral Wool is a semi-rigid stone wool insulation slab used for acoustic, thermal and fire insulation in walls, floors, ceilings, partitions and roof constructions. With a nominal density of 60kg/m³, RW3 is commonly used within soundproofing systems to absorb sound within cavities and reduce resonance.

Product Specification

Suitable Applications

ROCKWOOL RW3 25mm can be used in a wide range of acoustic, thermal and fire insulation applications. It is commonly installed within:

• Shallow stud walls and partition walls
• Slim wall lining systems
• Ceiling voids and suspended ceiling systems
• Service voids and boxed-in areas
• Drylining and acoustic wall systems
• Roof and general building insulation applications
• Home offices, studios, media rooms and commercial spaces

Acoustic Use

ROCKWOOL RW3 is used to help absorb sound within a wall, floor or ceiling cavity. Its stone wool fibre structure helps reduce sound movement inside the void and can improve the overall performance of a complete soundproofing system.

RW3 is mainly used to help with airborne noise, such as voices, TV noise, music and general room-to-room sound transfer. In floor and ceiling systems, it can also support the wider acoustic build-up by reducing resonance within the cavity.

Sound Absorption

ROCKWOOL’s RW Slabs datasheet lists RW3 at 25mm thickness with a practical sound absorption coefficient of 0.55 (H). This makes 25mm RW3 useful in shallow acoustic cavities where sound absorption is required but space is limited.

Common System Uses

• Inside slim acoustic wall linings
• Between timber studs where cavity depth is limited
• Within shallow ceiling voids
• Behind acoustic plasterboard systems
• Combined with Tecsound acoustic membranes
• Combined with resilient bars or furring channel systems
• Used with acoustic sealant to reduce weak points around edges and junctions

Important Performance Note

ROCKWOOL RW3 is an acoustic insulation slab, not a complete soundproofing system on its own. It performs best when used inside a full wall, floor or ceiling build-up with suitable acoustic boards, membranes, isolation products and properly sealed joints.

The final soundproofing result will depend on the existing structure, cavity depth, installation quality, surrounding materials and how well gaps and flanking paths are controlled.

Handling Advice

ROCKWOOL RW3 slabs can be cut to fit between studs, joists and other framing. For best results, cut the slabs neatly so they fit snugly within the cavity without being heavily compressed. Over-compressing mineral wool can reduce its effectiveness within the acoustic build-up.

If you are unsure whether 25mm RW3 is the correct thickness for your project, please contact our team before ordering. We can help advise on the most suitable insulation and soundproofing system for your room, noise issue and available cavity depth.

How to Install ROCKWOOL RW3 25mm Acoustic Mineral Wool

ROCKWOOL RW3 25mm Acoustic Mineral Wool is designed to be fitted into shallow wall, floor and ceiling cavities as part of an acoustic insulation system. It helps absorb sound inside the void, reduce resonance and support the overall performance of the full soundproofing build-up.

The 25mm thickness is useful where space is limited, such as slim wall linings, shallow cavities, service voids, media walls and other areas where thicker slabs may not fit. For best results, the slabs should be cut neatly and fitted snugly without being heavily compressed.

What You’ll Need

• ROCKWOOL RW3 25mm Acoustic Mineral Wool slabs
• Measuring tape
• Insulation saw or sharp serrated knife
• Straight edge or board for cutting
• Gloves
• Long-sleeved clothing
• Dust mask
• Safety glasses
• Waste bag for offcuts
• Acoustic sealant, if sealing around the system

Before You Start

Check the cavity depth before installing the slabs. ROCKWOOL RW3 25mm is best suited to shallow cavities that can accept a 25mm slab without excessive compression.

If the cavity is deeper, a thicker RW3 slab may be more suitable. If the cavity is shallower than 25mm, avoid forcing the slab into place, as over-compression can reduce the consistency and acoustic benefit of the installation.

Step 1: Prepare the Area

Before fitting the insulation, make sure the installation area is ready. The cavity or frame should be:

• Clean — remove dust, loose debris and leftover materials.
• Dry — avoid installing insulation into damp cavities.
• Clear — check for cables, pipework, fixings and other obstructions.
• Stable — make sure studs, battens, joists or framing are secure before fitting.

Take care around electrical cables, pipework and other services. Do not cut or damage existing services when fitting the slabs.

Step 2: Measure the Cavity

1. Measure the width and height of the cavity between studs, battens, joists or framing.
2. Check the cavity depth to confirm that 25mm RW3 is suitable.
3. Mark the required slab size before cutting.

For a secure friction fit, cut the slab slightly oversized by a few millimetres. This helps the insulation stay in position and reduces gaps around the edges.

Step 3: Cut the RW3 Slabs

1. Place the slab on a stable cutting surface.
2. Use a straight edge or board as a cutting guide.
3. Cut the slab using an insulation saw or sharp serrated knife.
4. Trim neatly around pipes, cables, sockets and awkward shapes where needed.

Clean, accurate cutting helps the slab fit properly and keeps the cavity evenly filled. Try to avoid leaving empty spaces around the edges of the installation area.

Step 4: Fit the Slabs into the Cavity

1. Place the cut slab into the cavity.
2. Push it gently into position.
3. Make sure it fits snugly between the framing or within the void.
4. Check that the slab fills the space evenly without being crushed.

The slab should sit securely in place, but it should not be heavily compressed. A neat friction fit is usually best for acoustic performance.

Step 5: Fill Gaps and Awkward Areas

Use offcuts to fill small gaps around edges, pipes, joists, battens and irregular spaces. The aim is to keep the cavity evenly filled with no obvious voids.

Sound can travel through weak points, so careful fitting around awkward areas can help improve the overall acoustic result.

Step 6: Add the Next Acoustic Layer

Once the RW3 is fitted, the next part of the soundproofing system can be installed. Depending on the project, this may include:

• Acoustic plasterboard
• Standard plasterboard
• TECSOUND acoustic membrane
• Resilient bars
• Furring channels
• Service void linings
• Acoustic sealant around edges and joints

ROCKWOOL RW3 performs best as part of a complete acoustic build-up. The insulation absorbs sound within the cavity, while boards, membranes and isolation products help add mass and reduce vibration transfer.

Installing RW3 25mm in Walls

For slim wall linings, media walls and shallow stud cavities, fit RW3 25mm between the battens or studs. Cut each slab to fit snugly, then install the chosen plasterboard or acoustic lining system over the frame.

For better soundproofing performance, RW3 is commonly combined with acoustic plasterboard, Tecsound membrane, resilient bars or furring channels depending on the wall construction.

Installing RW3 25mm in Ceilings

For shallow ceiling voids or ceiling lining systems, fit RW3 25mm between the framing or within the available void. Work carefully overhead and cut the slabs to manageable sizes where needed.

For improved ceiling soundproofing, RW3 is often used with resilient bars, furring channels, acoustic plasterboard, Tecsound membrane and acoustic sealant.

Installing RW3 25mm in Service Voids

RW3 25mm can be useful in service voids, boxed-in areas and shallow cavities where pipework, cables or other services are present. Cut carefully around services and fill the available space without crushing the slab.

Where noise is coming from pipes or services, RW3 may form part of the wider treatment, but pipe-specific products such as acoustic pipe wrap may also be required depending on the noise issue.

Installation Tips

• Wear PPE — use gloves, long sleeves, eye protection and a dust mask when cutting and fitting mineral wool.
• Cut slightly oversized — this helps the slabs friction-fit into the cavity.
• Avoid over-compression — heavily compressed insulation may reduce acoustic effectiveness.
• Fill the full cavity — avoid gaps around edges, battens, joists, pipes and cables.
• Use offcuts carefully — small pieces can fill awkward spaces and reduce waste.
• Choose the right thickness — 25mm RW3 is best for shallow cavities where deeper slabs are not practical.
• Use within a full system — combine with suitable acoustic boards, membranes and sealants for better results.

Important Soundproofing Note

ROCKWOOL RW3 is an acoustic insulation slab, not a complete soundproofing system by itself. It helps absorb sound inside the cavity, but the final result depends on the complete wall, floor or ceiling build-up.

For best results, combine RW3 with suitable acoustic boards, membranes, isolation products and acoustic sealant. If you are unsure whether RW3 25mm is the right thickness for your project, please contact our team before fitting. We can help advise on the most suitable system based on your room, cavity depth and noise issue.