mineral wool vs. wood fibre

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

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 Mool allow for pockets where air becomes trapped and thus acts as an insulator.


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 damp are reduced.

This is indeed the case for both Wood Fibre and Mineral Wool, as 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 damp 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 and preventing 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 insulation is an extremely sustainable and renewable material. We source our Wood Fibre Insulation boards from a company called Pavatex, who are 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 manufacture process aims to be as eco-friendly as possible. The finished boards are recyclable and compostable.

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

Fire Resistance

We source our Mineral Wool insulation boards from Rockwool, who offer 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 creates a barrier which stops oxygen passing through and feeding the flames, thereby slowing the spread of fire.

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