Knauf Rocksilk RS45

Knauf Rocksilk RS45 is a semi-rigid rock mineral wool slab made with Knauf’s ECOSE® binder technology. It easily fits between studs or joists. The slab provides acoustic, thermal, and fire resistance performance for floors, walls and partitions.

What Is Rocksilk RS45 Insulation?

RS45 insulation is a non-combustible rock mineral wool slab. It has a tested thermal conductivity (λ) of about 0.035 W/mK and a nominal density of 45 kg/m³. The slab is rated Euroclass A1 for reaction to fire. Its other notable features are that it:

• Resists rot
• Does not feed mould
• Offers lasting performance – can last as long as the wall stands

What Is RS45 Slabs Used For?

Here are the various ways RS45 Rocksilk insulation can be used:

• Light steel frame infill – RS45 slabs friction-fit into light steel studs in commercial or residential buildings to provide thermal and acoustic insulation.
• Timber frame wall cavities – The semi-rigid slabs fit between studs, and do not compress or sag.
• Used in internal partitions, separating floors, and built-up roofs that require acoustic and thermal performance.
• Internal partitions requiring improved sound absorption – The RS45 density helps reduce sound transmission between rooms.
• Separating floors / suspended timber ground floors – Used between floor joists in timber floors for thermal comfort and reduced footfall noise.
• Fabrication projects – Contractors sometimes cut RS45 slabs to produce bespoke insulation components, such as acoustic baffles or fire breaks within larger assemblies.
• Built-up roof systems – Can be used with vapour control layers and membranes as part of a layered roof insulation strategy.
• Fire separation zones – RS45 can be used in fire-rated constructions where non-combustible mineral wool is specified. However, the fire rating always depends on the tested system as a whole.
• It may be used in areas where fire performance is critical (like separating escape stair walls or around frames in multi-storey buildings). Check the specific fire strategy.

Benefits Of Rocksilk RS45

Some benefits of installing Knauf RS45 are:

• Keeps heat in due to its good thermal performance.
• Cuts airborne noise better than many foams (mineral wool is absorbent).
• Provides non-combustible insulation (Euroclass A1), contributing to fire-resistant construction when used within a tested system.
• It is stable – Water-repellent, moisture-stable, and does not rot. Also resists pests and mould.

FAQ

Where to buy Rocksilk RS45 insulation?

You can buy Rocksilk RS45 online from Insulation Wholesale. We stock a wide range of thicknesses and pack sizes at trade prices, with quick delivery options. Our product pages link to Knauf Rocksilk Insulation datasheets and safety sheets, so you receive the correct technical information with your order. Check delivery and lead times, and request a quote if you need bulk pricing.

How to cut RS45 insulation?

Score and slice with a sharp, insulated-board knife or handsaw for neat edges. For a tight fit in rainscreen or studwork, cut slightly oversize, then compress gently so the slab friction-fits. That reduces gaps and keeps thermal performance.

How good is RS45 insulation?

Knauf insulation Rocksilk RS45 is a high-performing mineral wool slab. It provides λ ≈ 0.035 W/m·K, excellent acoustic absorption, and strong fire performance (Euroclass A1), balancing thermal, acoustic, and fire performance in a single product. Match thickness to the U-value you need – the thicker the board, the higher its thermal resistance.