Introducing the Rockwool Flexi 100mm acoustic insulation slab — a specialist stone wool slab engineered for superb acoustic, thermal and fire-safety performance. With a thickness of 100 mm, and board dimensions of 1,200 mm × 600 mm, each pack covers approximately 4.32 m² (6 slabs per pack) for efficient coverage in wall, ceiling or floor systems.

This slab features the patented FLEXI Edge® — a flexible edge along one side of the board that ensures a snug friction fit within timber or metal frames, minimising gaps and improving installation integrity.

Thermally, the Flexi slab delivers a declared thermal conductivity of 0.038 W/m·K at this thickness, making it effective in slowing heat loss within framed cavity builds.

From an acoustic standpoint, the 100 mm depth gives added mass and thickness, which supports improved airborne sound reduction — ideal for partition walls, separating floors/ceilings and other noise-sensitive applications.

Fire safety is first-class: the product is rated Euroclass A1 (non-combustible) under BS EN 13501-1, giving you confidence in a fire-safe build.

Installation is straightforward: the slab is semi-rigid stone wool, easy to trim with a sharp knife, friction-fit between studs/joists, and the flexible edge helps maintain contact with the frame even when timber shrinks. Ensuring the cavity is fully filled, with no voids or gaps, maximises acoustic and thermal performance.

Applications include: interior stud partitions, separating walls between rooms/flats, ceilings above sound-sensitive areas, floors between dwellings or offices, and refurbishment projects where depth allows 100 mm slabs and performance must be strong.

Key Features

• Thickness: 100 mm — deep build-up for superior acoustic & thermal effect

• Board size: 1,200 mm × 600 mm (L×W)

• Coverage per pack: ~ 4.32 m² (6 slabs)

• Thermal conductivity (λD): ~ 0.038 W/m·K for 100 mm thickness

• Fire classification: Euroclass A1 (non-combustible)

• Material: Stone wool (rock mineral wool) — naturally fire-resistant, durable, dimensionally stable

• Patented FLEXI Edge® for tight friction-fit between frames, reducing gaps & waste

• Excellent acoustic performance: enhanced sound reduction between rooms/floors

• Suitable for framed construction: partitions, ceilings, floors, timber or metal studs

• Easy installation: cut to size, friction-fit, minimal sagging even with timber shrinkage