Knauff Rocksilk RS45 - Rock Mineral Wool

Knauf Rocksilk® RS45 Rock Mineral Wool Slabs | 600mm x 1200mm | 25mm / 50mm / 100mm

Knauf Rocksilk® RS45 is a rock mineral wool slab that combines sound absorption, thermal insulation, and fire protection in a single product. The mineral wool structure absorbs sound energy within wall, floor, and ceiling cavities — reducing both the reverberation within the cavity and the transmission of airborne noise through the overall assembly. Unlike a mass barrier such as MLV, which resists sound transmission through density, mineral wool works by converting sound energy into heat as it passes through the fibrous structure, making the two products complementary rather than interchangeable in a full acoustic build-up.

RS45 is non-combustible, achieving Euroclass A1 reaction to fire classification — the highest possible rating under EN 13501-1 — with a melting point in excess of 1000°C. It is manufactured using Knauf's ECOSE® Technology plant-based binder, replacing the petrochemical resins used in conventional mineral wool products. The 600mm slab width is designed to friction-fit between studs and joists at standard 600mm centres without cutting.

Three thickness options are available: 25mm, 50mm, and 100mm. The appropriate thickness is determined by the cavity depth of the build-up and the acoustic and thermal performance required by the specification.

Applications

• Internal walls and partitions — fit RS45 between the studs of timber or light steel frame partitions to increase the sound reduction of the wall assembly. An empty stud cavity allows sound to resonate freely and transmit through the structure; filling the cavity with mineral wool dampens this resonance and raises the Rw of the partition. 50mm is the standard specification for a 70mm or 100mm stud wall; 25mm suits shallower stud profiles or where partial fill is specified.
• Separating floors — fit between floor joists to reduce airborne sound transmission between floors and to dampen impact noise resonance within the floor void. 100mm is typically specified here to match standard 100mm joist depth and to maximise both acoustic and thermal performance within the floor build-up.
• Timber frame and light steel frame walls — RS45 is suited to both timber and light steel frame construction. The slab format maintains its shape and position within the frame without additional fixings, and the 600mm width eliminates the need to cut slabs to fit standard stud spacings.
• Ground floors — installed between ground floor joists to provide thermal insulation and reduce airborne sound transmission from below the floor. 100mm is standard for ground floor thermal specifications; acoustic performance is a secondary benefit in this application.
• Pitched roofs at rafter level — fitted between rafters as part of a warm or cold roof build-up where acoustic separation between the roof structure and the room below is required, or where thermal performance targets must be met at rafter level.
• Fabrication and general build-ups — the slab format and consistent density make RS45 suitable for fabricated panel systems, acoustic enclosures, and bespoke build-ups where a specified density mineral wool is required.

Product Benefits

• Euroclass A1 — non-combustible. A1 is the highest reaction to fire classification under EN 13501-1. RS45 will not contribute to the development or spread of fire and has a melting point in excess of 1000°C, providing longer periods of fire resistance than many mainstream insulants. This makes it suitable for use in fire-rated wall and floor assemblies where combustible insulation materials cannot be specified.
• Multi-function: acoustic, thermal, and fire in one product. RS45 replaces what would otherwise require separate acoustic and thermal insulation layers. Specifying a single product simplifies procurement, reduces the number of materials on site, and eliminates compatibility questions between separate acoustic and thermal layers.
• 600mm slab width — fits standard stud and joist centres. The 600mm slab width matches the standard structural spacing used in timber and light steel frame construction. Slabs friction-fit between members at 600mm centres without cutting, reducing installation time and offcut waste.
• Three thickness options — 25mm, 50mm, 100mm. Thickness selection is determined by cavity depth and performance requirement. 25mm suits shallow stud profiles and partial-fill specifications. 50mm is the standard cavity fill for most internal wall and partition applications. 100mm is used in separating floors, external walls, and build-ups where maximum acoustic and thermal performance is required.
• ECOSE® Technology plant-based binder. Manufactured using a bio-based binder derived from rapidly renewable materials, replacing the formaldehyde-containing resins used in conventional mineral wool. The result is a product with a lower embodied carbon footprint and no added formaldehyde.
• Consistent density and slab format. The slab format maintains its shape and position within a cavity without sagging or settlement over time, ensuring acoustic and thermal performance is retained throughout the life of the build-up.

Installation

Cut RS45 to size using a sharp serrated knife and straightedge. Wear gloves and a dust mask when handling mineral wool — fibres can cause skin and respiratory irritation. Friction-fit slabs between studs and joists at 600mm centres; the 600mm slab width is designed to hold in position without additional fixings in standard frame construction. Butt all joins tightly and ensure there are no gaps or voids within the cavity — any unfilled section reduces both acoustic and thermal performance across the assembly.

The Technical Details