Mycelium composites are grown rather than manufactured. What published research says about their insulating performance, and why fire safety, moisture and certification still limit their use.
Mycelium is the root-like network of fungi. Grown through agricultural by-products such as hemp hurds, straw or sawdust, it binds the loose material into a solid, lightweight composite. After growth, the material is dried or heat-treated to stop the fungus, leaving a block or panel that can be used as insulation or acoustic material. Because it is grown at low temperature from waste streams, mycelium insulation has attracted interest as a low-carbon alternative to conventional insulation.
How well does it insulate?
The key property of an insulation material is its thermal conductivity, expressed in watts per metre-kelvin (W/m·K): the lower the value, the better the insulation. For comparison, conventional products typically have the following values:
- mineral wool: roughly 0.032 to 0.040 W/m·K;
- expanded polystyrene (EPS): roughly 0.030 to 0.038 W/m·K;
- polyurethane and PIR boards: roughly 0.022 to 0.028 W/m·K.
Published laboratory studies of mycelium composites report higher values. A 2025 review in the journal Energies (doi:10.3390/en18164225) found reported thermal conductivities mostly in the range of about 0.036 to 0.06 W/m·K. Results depend strongly on the fungal species, the substrate, the density and the processing. Lower-density samples generally insulate better but are mechanically weaker.
In practical terms, the best mycelium composites approach mineral wool, while typical samples need a greater thickness to reach the same thermal resistance. In a deep renovation, where wall space is limited, that extra thickness matters.
Beyond thermal conductivity
Insulation has to do more than slow heat flow, and these other properties are where the evidence is thinnest.
- Fire. Building insulation must be classified for reaction to fire under EN 13501-1. Most published fire testing of mycelium composites has been at small or bench scale, and full-scale classification results are rare. Bio-based insulation products assessed so far often fall into the lower reaction-to-fire classes unless treated.
- Moisture. Mycelium composites absorb water, which can reduce their insulating performance and, in poorly designed constructions, raise the risk of mould or decay. Water resistance and long-term durability are identified as the main open questions in the research literature.
- Biological stability. The material must remain inert after treatment, without regrowth or degradation over the decades a building element is expected to last.
- Consistency. As a grown material, mycelium varies more from batch to batch than factory-made products. Process standardisation is still developing.
Certification: the practical barrier
Conventional insulation products are covered by harmonised European standards: EN 13162 for mineral wool and EN 13163 for EPS, for example. There is no harmonised standard for mycelium insulation. To carry a CE marking, a manufacturer would need a European Technical Assessment, based on a European Assessment Document. Several plant-fibre insulation products, such as hemp, have taken this route. For mycelium, few if any products have so far completed it. Without that documentation, designers and insurers are unlikely to specify the material for walls and roofs.
Research and demonstration projects, including EU-funded projects on bio-based building materials, are generating the test data needed. A small number of companies in Europe and North America produce mycelium panels, mostly for acoustic and interior uses where fire and moisture requirements are less demanding.
Where it could fit
The case for mycelium insulation rests mainly on its low embodied carbon, its use of agricultural waste and its compostability at the end of its life. Those advantages will matter more as the recast Energy Performance of Buildings Directive requires the life-cycle global warming potential of new buildings to be calculated and disclosed: from 2028 for buildings above 1,000 m², and from 2030 for all new buildings. Materials with low embodied carbon will then show up directly in a building’s energy performance certificate.
For now, mycelium is best seen as a promising material at an early stage. It is suited to interior and acoustic applications and to pilot projects. Wider use in building envelopes will depend on fire classification, moisture performance and certified products. For the role of insulation in meeting the zero-emission building standard, see our explainer; for heating technology, see heat pump supply chains.