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Knauf Insulation: Technical Column

by Jennie Ward

Glass or Rock Mineral Wool Insulation – what’s best where?

Mineral Wool insulation is extremely versatile and can be used to enhance the thermal and acoustic performance, comfort and fire safety of a building, but which is better, Glass or Rock Mineral Wool? In our new column, Bradley Hirst, Technical Services Manager from Knauf Insulation, explains why you should always consider the performance and application first.

Compressive strength Rock Mineral Wool has shorter strands than Glass Mineral Wool, giving it superior compressive strength, so should always be used where robustness is required, such as warm flat roofs and external walls. Some of our Rock Mineral Wool products are manufactured using Krimpact Technology which provides consistent density throughout, combined with superior impact and compression resistance.

Thermal performance Glass Mineral Wool offers better thermal performance in some products and can achieve a lambda value of 0.032 W/mK, compared to a best of 0.034 W/mK for Rock Mineral Wool. For applications where thermal performance is the primary factor, such as insulating masonry cavity walls or lofts, Glass Mineral Wool is the best option.

Fire safety Glass and Rock Mineral Wool are naturally non-combustible and will not contribute to the development or spread of fire. This means they comply with building regulations banning the use of combustible materials on high-rise buildings, and are the safest option at any height.

With a melting temperature of over 1,000ºC, Rock Mineral Wool minimises heat transfer, making it more suitable for applications where fire resistance is required, such as the separating floor in a loft conversion. Products developed for fire resistance are rigorously tested to provide containment of a fire for a specified period of time, giving occupants time to escape.

Glass Mineral Wool has superior tear strength so can be made into acoustic rolls and cut to the exact length of the wall, minimising gaps where sound could permeate.

Reducing noise Mineral Wool offers better sound absorption and reduction than other insulants, but many people believe Rock Mineral Wool’s higher density means it performs better than Glass Mineral Wool. Our tests show Glass and Rock Mineral Wool perform equally well in acoustic applications in real world buildings. Glass Mineral Wool has superior tear strength so can be made into acoustic rolls and cut to the exact length of the wall, minimising gaps where sound could permeate. This makes it ideal for internal walls.

Comfort Both Glass and Rock Mineral Wool can also contribute to installer’s comfort. Products that are manufactured with ECOSE Technology, Knauf Insulation’s unique bio-based binder, contain no added formaldehyde or phenol. This means they are soft to touch and easy to handle. They generate low levels of dust and VOCs and have been awarded the Eurofins Gold Certificate for Indoor Air Comfort and most recently the Declare ‘Red List Free’ label.


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