Blog

Mineral wool is a widely used open cell insulation material created by melting rock or industrial slag and spinning it into fine, wool-like fibres.

The term ‘Open Cell Cavity Insulation’ is another phrase used to typically describe these types of materials.

Although quite a bulky and thick material, it is valued for its thermal insulation, soundproofing abilities, and resistance to fire, making it suitable for use in cavities within building construction, pipe insulation, and various other industrial applications.

It’s one of the most widely used and effective forms of insulation found in modern construction, particularly in homes and buildings that require not just thermal efficiency, but also sound control.

While it’s often thought of as a general-purpose insulator, mineral wool plays a crucial role in acoustic absorption, especially when installed in framed cavity walls made from timber or aluminium stud, as well as between floor joist systems.

History of Mineral Wool

Mineral wool dates back to the late 19th century, when it was first discovered in volcanic areas as a natural by-product of lava cooling rapidly in strong wind.

This formed thin, wool-like fibres, hence the name.

The industrial production of mineral wool began shortly thereafter, with manufacturers realising that molten rock or slag could be spun into fibres mechanically, creating an insulating material that was lightweight, fire-resistant, and excellent at trapping air.

Over time, the formulation was refined to improve its consistency, density, and suitability for specific applications, including acoustic insulation.

How Does It Work?

Mineral wool works by trapping air within a dense matrix of fibrous material.

When used for thermal insulation, it slows down the movement of warm air through walls, ceilings and floors, relying predominantly on its own depth of material to achieve thermal resistance and a slowing of thermal creep.

Thermal Conductivity values can vary from around the 0.038W/mK to 0.032W/mK which is applied in thicknesses usually from 25mm, 50mm 75mm or 100mm.

When needing to arrest and eliminate thermal bridging in much thinner tolerances and spaces, it is essential to use a thermally insulating material with lower thermal conductivity values.

Thermablok Aerogel Ltd, our sister company has such materials.

Thermablok Aerogel A2 10mm Insulation Blanket (A2-s1,d0) is a nano particle aerogel which is non combustible with a thermal conductivity of 0.016W/mK, the lowest possible.

It is used in increments of 10mm to insulate many types of issues within construction where space is at a premium and tight tolerances reduce the thickness of material that can be installed.

These include all sorts of applications internally and externally, from steel frames, bifold doors, walls, window reveals, dormers, balconies, roofs and  floors for example.

But back to Open Cell / Mineral Wool – the materials properties, varying densities and increasing thicknesses also enable it to be a sound absorber.

Sound waves are essentially vibrations travelling through the air.

When those waves enter a cavity wall, they pass through the fibres of the mineral wool.

The fibrous structure disrupts the sound energy and absorbs the sound waves, thereby reducing the power, reach and penetration of the sound.

The results will vary depending on depth and density and an increasing noise reduction coefficient (NRC) of the cavity fill used, creating a noticeable drop in noise transmission from one room to another, especially when combined with other specialist soundproofing materials like Acoustiblok Isolation Membrane or Acoustic Sealant.

For more information on Noise Reduction Coefficient (NRC) please see our earlier blog. (add link)

But open cell cavity fill should not only be recognised for the properties of acoustic absorption it offers when installed into a cavity.

Consideration should be given to what would happen if a cavity is left open / empty and the increased resonance that would result.

So worth remembering that the cavity insulation brings a positive value by being installed but also prevents what would be a negative value as well if it were not to be installed.

Types of Mineral Wool Insulation

Mineral wool isn’t a single material, but a category that includes several variants.

Each is suited to different environments and performance requirements:

Alkaline Earth Silicate Wool (AES Wool)

This is a low-bio-persistence mineral wool often used in high-temperature environments, but it also finds application in buildings where minimal irritation and environmental impact are important.

It’s less common in general soundproofing applications.

Alumino Silicate Wool (ASW)

Made from alumina and silica, ASW is highly resistant to heat and is mostly used in industrial furnaces and kilns.

Its acoustic benefits are limited compared to more conventional mineral wools.

Polycrystalline Wool (PCW)

Polycrystalline wool is extremely heat-resistant, often used in aerospace and specialist industrial settings.

It’s not typically found in residential or commercial construction due to cost.

Kaowool

Kaowool is a brand name often used generically for ceramic-based insulation.

It offers some acoustic dampening properties, but like ASW and PCW, its main role is thermal resistance at extreme temperatures rather than soundproofing.

For general building applications, particularly for sound reduction in cavity walls, the more practical and cost-effective solutions are those based on stone wool or slag wool, such as Acoustiblok Quietfibre.

Common Mineral Wool Insulation Brands

Several brands dominate the mineral wool space, each with different strengths.

Here’s how they compare, especially in acoustic applications:

Rockwool

Rockwool is a household name in the insulation world and offers a wide range of stone wool products.

These are often used in general construction for stud walls and flooring systems to improve thermal and acoustic insulation levels.

Acoustiblok

Acoustiblok Quietfibre is a mineral wool specifically designed and well recognised for use in high-performance sound installations such as AV / Cinema for acoustic absorption and reducing of resonance and regeneration of energy.

Quietfibre is made for use within timber or aluminium stud cavity walls as well as flooring systems such as tiered staging, making it ideal for studios, home cinemas, offices, or any environment where sound control is a priority.

It’s designed to work seamlessly alongside Acoustiblok Isolation Membrane, Acoustigrip Jointing Tape, and Acoustic Sealant, to give a complete, integrated soundproofing system.

Acoustiblok QuietFibre is also used as a core which, when wrapped in a wide range of fabric finishes, create frameless AcoustiWall Absorber Panels and AcoustiCloud Ceiling Absorber Panels to absorb echo and resonance thereby vastly improving lively room acoustics.

Knauf

Knauf offers a range of glass and mineral wool insulation products.

While these have the obvious acoustic properties by absorption and reduction of an increase in resonance, they’re generally aimed at thermal insulation first and foremost, with acoustic performance as a secondary benefit.

Superglass

Superglass is another insulation manufacturer with mineral wool products.

Soundproofing Performance of Mineral Wool

When it comes to soundproofing framed cavity walls, mineral wool insulation plays a critical role; but only when used correctly.

The fibres in mineral wool absorb airborne sound waves, significantly reducing echo and transmission between rooms.

However, it’s important to note that absorption is not the same as isolation.

To achieve full-spectrum soundproofing, reducing both airborne and impact noise, mineral wool must be part of a broader system.

For example, in a timber stud wall, Acoustiblok Quietfibre performs best when friction-fitted between the studs, combined with Acoustiblok 3mm Isolation Membrane on one or both wall faces.

Gaps and joints should be sealed with Acoustiblok Acoustic Sealant and Jointing Tape to prevent sound flanking through tiny crevices.

In this setup, Acoustiblok Quietfibre’s high density helps to dampen mid to high-frequency noise, such as speech, music, and TV sound, while the Acoustiblok 3mm Isolation Membrane blocks low-frequency vibrations and structural noise.

Both play a vital role.

Acoustiblok Quietfibre cavity fill offers acoustic absorption between a stud frame as well as reducing resonance and regeneration of the original soundwaves, which occur if allowed to enter an otherwise empty, hollow and cave like cavity.

Acoustiblok Isolation Membrane plays a vital part of thermally converting acoustic energy across the entire wall surface, therefore over the specified mineral wool cavity insulation and critically over the stud framing to reduce the resulting flanking transmission which would occur through a structure’s own rigidity.

This layered approach is far more effective than relying on mineral wool alone in the cavity and hoping for the best by simply boarding over with a finishing board of choice.

A suitable frame for the obvious need for structure and a principle of decoupling.

Full fill / part fill as specified of Acoustiblok Quietfibre for absorption, a noise reduction coefficient and reducing resonance / regeneration.

A complete lining across the entire structure with Acoustiblok Isolation Membrane for thermal conversion of acoustic energy to reduce penetration, vibration and flanking transmissions.

A finishing board of choice which adds mass and density and therefore a principle of deflection.

The result – transforming a standard partition wall which simply divides a space into a barrier that dramatically reduces unwanted noise transmission, all without significantly increasing wall thickness.

Summary

So, what is mineral wool insulation? In short, it’s a dense, fibrous material made from molten rock or industrial slag, designed to trap air and reduce heat and sound transfer.

While it’s long been valued for thermal insulation, its role in soundproofing framed cavity walls is just as important, especially when used as part of a complete system.

Among the options available today, Acoustiblok Quietfibre offers a professional-grade open cell wool solution specifically tailored for acoustic performance.

Designed with sound absorption at its core, it integrates perfectly with other soundproofing components to create quiet, comfortable spaces in both residential and commercial settings.

If you are serious about noise control, especially in partition walls constructed from timber or aluminium studs, Acoustiblok Quietfibre should be your go-to choice.

Not only because it’s effective, but because it is engineered for soundproofing, not just insulation.

Want to know more? Contact our expert soundproofing team for further details.