Mineral wool insulation looks soft and lightweight, but it begins with hard mineral-based raw materials.
Those materials are processed into fine fibres, which are then formed into rolls, slabs or other insulation products.
What goes into the insulation depends on which type of mineral wool is being made.
Quick answer: Mineral wool is made by turning mineral-based raw materials into fine fibres. Glass mineral wool is made from glass-based materials, often including recycled glass, while stone wool is made from rock-based materials.
Why is it called mineral wool?
The name comes from two things.
“Mineral” refers to the type of raw material used.
“Wool” describes the fibrous texture of the finished insulation.
It is not wool in the same sense as sheep’s wool. The fibres are manufactured rather than grown naturally.
What is glass mineral wool made from?
Glass mineral wool is produced from glass-based raw materials that are melted and formed into fine fibres.
Modern products can also make use of recycled glass as part of that process.
This is especially relevant to products such as Knauf mineral wool insulation, where glass-based fibres are used to create the familiar lightweight loft-roll structure.
Does Knauf use recycled material?
Yes, recycled glass forms part of the raw-material mix used in modern glass mineral wool manufacture.
That means materials which would otherwise remain in the waste stream can be incorporated into new insulation products.
The exact recycled content can vary between products and manufacturing specifications, so it is better to look at the current product information than assume one percentage applies across every range.
What happens to the glass?
The raw materials are processed at high temperature and turned into a molten form.
That material is then transformed into extremely fine fibres.
Those fibres are arranged into a light, open structure containing large numbers of small air spaces.
That is what gives glass mineral wool its familiar soft, springy appearance.
Why add a binder?
The fibres need to hold together in a stable product.
A binder helps maintain the shape and integrity of the insulation so that it can be manufactured, transported and installed effectively.
Modern mineral wool products use carefully developed binder systems rather than simply loose fibres.
What is stone wool made from?
Stone wool uses rock-based raw materials rather than glass-based ones.
The overall principle is similar: mineral material is melted and formed into fibres.
The finished material is still part of the mineral wool family, but it has different physical characteristics from glass mineral wool.
So are glass wool and stone wool the same?
No.
They belong to the same broad insulation family, but they are made from different raw materials and can be produced for different applications.
| Type | Main raw material | Typical form |
|---|---|---|
| Glass mineral wool | Glass-based raw materials, often including recycled glass | Lightweight rolls and slabs |
| Stone wool | Rock-based mineral materials | Usually denser slabs, batts or rolls |
Why does the finished material look nothing like glass?
Because the material has been completely transformed.
Instead of remaining as a solid sheet, the glass is converted into very fine fibres.
Those fibres create a large volume of trapped air, which is central to the insulation’s thermal performance.
Is recycled glass the reason mineral wool works?
No.
The thermal performance comes mainly from the fibrous structure and the air trapped within it.
Recycled content relates more to the way the product is manufactured and the materials used to make it.
Both points matter, but they are different.
How did modern mineral wool develop from older fibreglass?
Older fibreglass products helped establish the idea of lightweight glass-fibre insulation in UK homes.
Modern manufacturing has refined the fibres, binders, packaging and product ranges substantially.
Our earlier guide on how glass-fibre insulation became common looks at that history in more detail.
You can also read about the development of modern glass mineral wool.
Does every mineral wool product use the same recipe?
No.
Different manufacturers and product ranges can use different:
- raw-material mixes
- fibre structures
- binders
- densities
- thicknesses
- intended applications
That is why it is more accurate to think in terms of product families rather than assuming every mineral wool roll is identical.
Why does the manufacturing process matter?
The final performance depends on more than simply having glass or stone in the raw material.
The way the fibres are formed, arranged and held together influences the finished product and what it is designed to do.
Raw materials
Glass-based or stone-based materials form the starting point.
Fibres
The material is transformed into extremely fine strands.
Air spaces
The fibre network creates the trapped air that helps reduce heat transfer.
Finished product
The fibres are formed into rolls, slabs or other products for specific uses.
So what is in the roll in your loft?
If the material is glass mineral wool, it is essentially a carefully manufactured network of mineral fibres and trapped air created from glass-based raw materials.
It may look simple, but there is a lot of material science behind the fluffy roll most homeowners recognise.
Frequently asked questions
What is mineral wool made from?
It is made from mineral-based raw materials that are processed into fine fibres. The raw materials vary depending on the type of mineral wool.
Is glass mineral wool made from recycled glass?
Modern glass mineral wool can include recycled glass within its raw-material mix.
Is mineral wool made from sheep’s wool?
No. The word “wool” refers to the fibrous appearance of the material, not an animal-based raw material.
Is stone wool the same as glass wool?
No. Both are mineral wool, but glass wool uses glass-based raw materials while stone wool uses rock-based materials.
Does recycled content make mineral wool insulate better?
No. Thermal performance mainly comes from the fibre structure and trapped air rather than the fact that some raw material is recycled.
In the next article: Mineral wool, glass wool and fibreglass are often used as if they mean the same thing. So what is the actual difference?
Read: What Is The Difference Between Mineral Wool And Fibreglass Insulation?
