Last edited 24 Jan 2021

Mineral wool

Mineral wool is a wide-ranging term which describes fibrous, spun yarn materials used as insulation in construction and other sectors. Depending on the mineral used and the process employed, it also goes by names, such as glass wool, stone wool, slag wool, mineral fibre (or fiber), mineral cotton, man-made vitreous fibre and man-made mineral fibre.

Although first produced commercially in 1871 in Osnabruck, Germany, the rock wool insulation industry was initiated in the US in 1897 when Charles Hall was able to convert molten rock into fibres.

Mineral wool applications in construction include:

As thermal insulation: in masonry cavity-walls, timber frame construction, and for roof spaces, also, in stud-partition walls and flat roofs, as well as for pipework and ductwork.
As acoustic insulation to resist the transmission of sound through partition walls and storey floors.
As fire insulation.
To absorb water and air to help root growth and nutrient uptake in hydroponics – ie, growing plants without soil using only solutions and minerals.

Properties:

Because it is porous with an open fibre structure, mineral wool traps air, making it highly efficient as an insulation material. A representative lambda (λ) value for it would be around 0.03W-0.04/mK.
The wool’s porous nature also makes it a good noise absorber. It is also incombustible and does not fuel the spread of flame.
Mineral wool is not prone to thermal ageing, which means it can retain its insulating properties for as long as it is in service.
Mineral wool does not sustain vermin and is highly resistant to the growth of mould, fungi or bacteria.
Glass and rock mineral wool insulation may be completely non-combustible (Euroclass A1 fire rating (non-combustible material’)) and can slow the spread of flame – this can allow a building’s occupants extra time to escape.
Mineral wool also has low thermal conductivity and resists the passage of sound. It is highly resistant to expansion and shrinkage which results in joints that stay as close as possible. It is also relatively inexpensive

The two main variants of mineral wool are stone wool and glass wool.

Glass wool is typically, manufactured by spinning or drawing a yarn of melted glass; a binder is used to form the glass fibres into a wool-type consistency. It can be produced as rolls, slabs, applied in-situ or sprayed.

Rock or stone wool is made from molten rock materials (such as ceramics or slag cast-offs – a by-product of the smelting process). It is made by blowing a stream of air through molten rock at a temperature of around 1,600°C. The result is very fine strands which are combined to create a wool-type material; alternatively, stone wool can be made by a process analogous to that of making candy floss – the molten rock is spun at high speeds and the threads drawn off. Typically, they will have a diameter in the range of 2-6 microns (millionths of a metre). They are then amalgamated to produce the characteristic woolly structure which can be compressed into boards, mineral wool batts or other forms. In its loose form, the wool can be blown into cavity walls and roof void spaces.