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Wood Fibre vs. Mineral Wool EWI

Surprisingly, when it comes to comparing insulation materials it isn’t all about how well they insulate. Thermal performance obviously comes into play, but there are other important factors to consider when choosing an insulation material for your EWI system.

At EWI Store, we offer five kinds of insulation materials: XPS, EPS, Kingspan K5, Wood Fibre and Mineral Wool. In today’s blog post, we’re going to go in-depth by taking a look at how Mineral Wool and Wood Fibre compare when placed side by side. 

Thermal performance – Mineral Wool comes out on top

Wood Fibre offers excellent performance with its thermal conductivity of 0.043 [W/(mK)]. As well as this, Wood Fibre also offers something called a decrement delay, which is how long it takes for the energy of the sun to pass through. Many people think that all insulation keeps you cool in the summer, which is a myth. However, Wood Fibre does and this decrement delay depends on the thickness of the board.

On the other hand, Mineral Wool insulation has a thermal conductivity of 0.036 [W/(m2K)]. One of the key benefits of choosing to install a mineral wool system is that not only is it a fantastic thermal insulator, but Mineral Wool also offers acoustic insulation. This is because of the fact that the material is so hard-wearing. The fibres within the Mineral Wool allow for pockets where air becomes trapped and thus acts as an insulator.

Breathability – Even performance

In breathable systems, the insulation materials are arranged in such a way that the layers become increasingly more vapour permeable from the inside to the outside so that moisture can safely escape from within the house. This creates a harmonious climate within the house where moisture and the risk of dampness are reduced.

This is indeed the case for both Wood Fibre and Mineral Wool. Both types of insulation are breathable and are made of layers with different densities.

Due to its excellent breathability, Wood Fibre Insulation is perfect when used with a timber frame property, because it is a vapour-open building material. It’s essential for a building to be able to breathe in order to prevent dampness and maintain structural integrity. Wood Fibre insulation is able to regulate the passage of water through the building structure, allowing for the diffusion of water vapour. This also prevents any detrimental moisture build-up within the property and the EWI system.

On the other hand, Mineral Wool insulation is also a vapour-open material, offering increased breathability. The presence of fibres and water-repelling compounds within the Mineral Wool wick moisture and water vapour through the material away from the substrate, allowing it to escape. Mineral Wool is non-hygroscopic, which basically means that it pushes water away.

Environmental impact – Wood Fibre is marginally better

Wood Fibre insulation is an extremely sustainable and renewable material. We source our Wood Fibre Insulation boards from a company called Pavatex, which is certified by the renowned nature plus standard – the European quality standard for building materials set up by the WWF, FSC and Greenpeace.

All of the timber used for their Diffutherm Wood Fibre Insulation boards comes from waste timber cuttings and their entire manufacturing process aims to be as eco-friendly as possible. The finished boards are therefore recyclable and compostable.

Rockwool is also made from a renewable, naturally occurring resource – volcanic rock. The insulation boards themselves are also 97% recyclable. Whilst slightly less than Wood Fibre’s status as 100% recyclable and compostable, still impressive!

Fire resistance – a clear win for Mineral Wool

We source our Mineral Wool insulation boards from Rockwool, which offers the most non-combustible insulation material on the market. The boards have the highest Euroclass Fire Rating of A1 and are even installed as a firebreak on high-rise buildings with EWI.

The Fire Resistance of Wood Fibre Insulation is rated at Class E, which is very similar to other insulating materials. However, Pavatex state that their Diffutherm Wood Fibre Insulation goes above other insulating materials because of the fact that it slows down the spread of fire. This is because the Wood Fibre is timber, which chars instead of burning. The charred exterior of the board also creates a barrier which stops oxygen from passing through and feeding the flames. Consequently, the spread of fire is slowed.

fire resistance as part of the 7 strengths of stone for mineral wool as opposed to wood fibre
Rockwool’s 7 Strengths of Stone

Acoustic performance

Mineral wool insulation has a porous and fibrous structure which gives it excellent sound absorption capabilities. The fibre structure traps air and attenuates sound waves, reducing the transmission of airborne noise such as speech, TV, and music. In addition, it can also reduce the transmission of impact noise, such as footsteps or items being dropped on the floor above.

The sound absorption capability is measured in terms of a Noise Reduction Coefficient (NRC). The NRC is a scalar representation of the amount of sound energy absorbed upon striking a particular surface. An NRC of 0 indicates perfect reflection; an NRC of 1 indicates perfect absorption. Mineral wool typically has an NRC rating of around 0.9 to 1.0, indicating it absorbs nearly all sound hitting it.

Wood fibre insulation also provides good sound absorption due to the porous structure of the material. The fibrous nature of the material converts sound energy into heat energy, effectively dampening sound transmission.

However, the acoustic performance of wood fibre insulation is slightly lower compared to mineral wool. This is due to the nature of the material and how it interacts with sound waves. Wood fibre insulation absorbs sound effectively. However, the denser nature of this material can sometimes lead to more sound reflection compared to mineral wool.

Its NRC rating can range widely depending on the specific product and its density. It typically falls somewhere between 0.6 and 0.85.

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4 thoughts on “Wood Fibre vs. Mineral Wool EWI

    1. Hi Kevin, wood fibre insulation, sourced from renewable forests and requiring less energy to produce, is generally more sustainable. Mineral wool, made from abundant but non-renewable materials, has a higher environmental impact despite the use of some recycled content.

  1. Which one is saver and healthier? Is there a possibility that in the future Mineral Wool could be classified as dangerous like what have happened to asbestos?

    1. Hi Spike, wood fibre is always likely to be safer and healthier, mainly due to the handling. Mineral wool can be a mild irritant when handled, so gloves and other general PPE is recommended. Both are typically free from VOCs so fine on the emissions front.

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