Rockwool Acoustic Sound Insulation Slab (RW-series & Flexi)

Rockwool RW3

RW3 is a medium-density stone wool slab engineered for acoustic control and balanced thermal performance in internal partitions and service walls. Its fibre structure absorbs airborne sound, limits reverberation and maintains stable performance in stud walls and suspended floor systems. RW3 suits residential and commercial spaces needing reliable acoustic comfort without heavy loading.

Rockwool RW5

RW5 is a high-density acoustic slab designed for demanding applications requiring maximum sound reduction, impact noise control and enhanced rigidity. Its dense stone wool core increases mass and dampens transmission in cinema rooms, plant areas, industrial partitions and high-performance wall systems. RW5 suits environments where high STC results and structural rigidity are essential.

Rockwool RWA45

RWA45 is a multi-purpose acoustic and thermal slab used widely across domestic and light-commercial builds. It delivers strong sound absorption within stud walls, joist zones and ceiling voids. Its ease of handling and reliable fit make it a preferred choice for general building insulation, renovation and mixed-use acoustic systems.

Rockwool Flexi

Flexi is a semi-rigid stone wool slab with a flexible edge strip designed for tight friction fit between studs, rafters and floor joists. The Flexi edge maintains compression, ensuring gap-free installation and continuous acoustic and thermal performance across uneven frames. Flexi is ideal for fast installation, refurbishment work and timber-frame projects.

Installation Guide:

• Measure and cut slabs with a long-bladed knife or insulation saw

• Insert slabs snugly into stud bays, rafters or joist zones under light compression

• Maintain continuous contact at edges to prevent acoustic leakage

• Seal gaps and junctions according to system requirements

• Keep insulation dry before installation and protect from weather exposure

Which One Should You Choose?

• RW3 - Best all-round balance

Suitable for homeowners and builders needing strong acoustic performance with moderate density. Ideal for partitions, floors and ceilings in most homes.

• RW5 - Maximum acoustic performance

Choose RW5 when you need premium noise control, higher density and improved sound attenuation. Best for studios, plant rooms, commercial partitions and high-performance systems.

• RWA45 - Most versatile option

Suited for general building work, mixed acoustic and thermal needs, and multi-application use. Ideal for standard residential and light-commercial projects.

• Flexi - Fast, friction-fit installation

Pick Flexi when your frames have irregular spacing or you need guaranteed edge pressure and gap-free installation. Perfect for timber frames, lofts and refurbishments.

What is the difference between Rockwool RW3, RW5 and RWA45 insulation slabs?

The main difference between Rockwool RW3, RW5, and RWA45 insulation slabs lies in their density, acoustic performance, and thermal efficiency, which determine where and why each type is best used. All three are made from high-quality mineral wool, offering excellent fire resistance, sound absorption, and thermal insulation, but they are designed for slightly different applications depending on performance needs.

• Rockwool RW3 has a medium density (around 60 kg/m³), providing a balanced mix of thermal and acoustic insulation ideal for walls, floors, and ceilings in both domestic and commercial buildings. It’s lightweight, easy to handle, and perfect for general-purpose use where moderate sound control and heat retention are required.

• Rockwool RW5 offers a higher density (around 100 kg/m³), giving it superior soundproofing and mechanical strength. It’s typically used in plant rooms, machinery enclosures, and partition walls where robust acoustic insulation and durability are essential. Its dense structure also improves fire resistance and dimensional stability, making it suitable for demanding environments.

• Rockwool RWA45, on the other hand, is the most versatile and cost-effective option, with a density of around 45 kg/m³. It provides dependable thermal insulation and noise reduction for domestic walls, stud partitions, and loft conversions. This makes it a popular choice for homeowners and builders seeking reliable performance at a lower weight and cost.

In short:

• Choose RWA45 for standard sound and thermal insulation in homes.

• Choose RW3 for balanced performance in mixed-use or commercial projects.

• Choose RW5 for maximum acoustic control and durability in high-performance applications.

Each product maintains the A1 fire rating and non-combustible properties Rockwool is known for, ensuring long-term safety and energy efficiency in any project.

Which Rockwool RW insulation is easiest to install?

Rockwool Flexi is the easiest to install because its flexible edge compresses into gaps and adjusts to uneven stud spacing. This gives a tight fit without careful trimming, making it ideal for DIY users and fast timber-frame work. RW3, RWA45 and RW5 install well too, but they need more precise cutting and handling because they have fixed edges. Among RW-series,

• RWA45: Easiest among the RW slabs because it’s lighter and simpler to cut for standard partitions.

• RW3: Moderate difficulty; slightly denser than RWA45 but still manageable for most installers.

• RW5: Hardest to install because its higher density makes it heavier and tougher to cut.

What is the difference between Rockwool RW slabs and Rockwool Flexi?

RW slabs offer fixed-density boards for controlled acoustic and thermal performance in standard stud layouts. Flexi provides a flexible edge that adapts to irregular spacing, making it more forgiving in refurbishment or timber-frame projects. Choose RW slabs for defined density performance; choose Flexi for quicker fitting and gap-free results.