Wood Fiber Insulation by Steico – Properties, Advantages, and Disadvantages [2025]

Mineral wool has a thermal conductivity coefficient Lambda [λ] of approx. 0.036 W/(mK), or even lower, depending on the material class. The specific heat capacity of mineral wool ranges around 800–1000 [J/(kgK)].

In comparison, wood fiber insulation has a thermal conductivity Lambda [λ] of approx. 0.036–0.038 W/(mK), and a specific heat capacity of approx. 2100 [J/(kgK)].

• What do these parameters mean? In short, the lower the Lambda [λ], the better the material retains heat. Comparing this parameter, mineral wool has a slightly better value, but the difference is not significant. These materials can therefore be considered comparable in terms of thermal conductivity.
• When comparing specific heat capacity (also known as specific heat [Cw]), wood fiber insulation outperforms mineral wool. This parameter indicates how much thermal energy the insulation material can absorb and how long it takes to release this energy into the building. In practice, high specific heat means that the building retains heat longer in winter (walls are better protected from external frost) and stays cooler in summer (walls are better protected from external heat). In summary, a house insulated with wood fiber will retain heat longer in winter and heat up more slowly in summer.
• Due to its high density, wood fiber is also more moisture-resistant and settles more slowly within the wall cavity compared to mineral wool. Up to 20% moisture content does not change the thermal conductivity of wood fiber. In practice, even damp wood fiber insulation can evaporate water in the summer and return to its natural structure – unlike mineral wool, which sags and forms thermal bridges. For insulation meant to last decades, this parameter is worth noting.
• Surprisingly, wood fiber insulation is also fire-resistant. It is enriched with a natural fire retardant – ammonium sulfate. When in contact with fire, the fiber forms a char layer that prevents the spread of flames and quick burnout. On the Steico website, one can find a video comparing how wood fiber performs against other insulation materials when exposed to fire.
• Wood fiber mats (e.g., Steico Flex) are much denser than standard mineral wool, making them better acoustic insulators. When using blown-in wood fiber (Steico Zell), the material can be compacted to levels practically unmatched by other insulation materials. The standard density for Steico Zell blown-in fiber is 45 kg/m³ for prefabricated walls. By adjusting the density during application, one can create a wall meeting even the demands of sound studios, cinemas, or playrooms.
• The last comparison criterion is price. Unfortunately, wood fiber performs worse in this respect. When comparing wood fiber mats (e.g., Steico Flex) to mineral wool rolls, wood fiber is significantly more expensive.