Evaluation of mycelium-based composites grown on sunflower seed shell and oat husk substrates inoculated with Trametes versicolor and Pleurotus ostreatus

Conventional synthetic insulation materials are predominantly petrochemical-based, non-biodegradable and contribute significantly to carbon emissions, thereby increasing the environmental footprint of the construction sector. Accordingly, mycelium-based composites (MBCs) have emerged as a sustainable alternative. Mycelium, the root-like network of fungal hyphae, acts as a natural binder when cultivated on lignocellulosic agricultural residues, forming lightweight, biodegradable composites. This study explored the potential of two agricultural by-products abundantly available in many regions worldwide, namely sunflower seed shells (SF) and oat husks (OH), as substrates for MBCs production. SF was investigated for the first time as a new primary substrate, while OH-based composites underwent detailed characterization due to limited existing research on cold climate agro-residues. Three substrate formulations were prepared: 100% SF, 50% SF–50% OH, and 100% OH. Also, two selective white-rot fungal species, Trametes versicolor and Pleurotus ostreatus , were used for inoculation. The combination of T. versicolor with these substrates was also studied for the first time, potentially enabling optimization of the mechanical and physical properties of the resulting MBCs. Key performance indicators included mechanical strength, thermal conductivity, water absorption, and dimensional stability under both dry and wet conditions. SF-based composites demonstrated superior mechanical and thermal performance, with a density of 173 kg/m 3 , thermal conductivity of 0.05 W/mK at a mean temperature of 4.5°C, and flexural strength of 221 kPa. In contrast, OH-based composites exhibited lower water absorption and improved dimensional stability in humid conditions, with minimal volumetric swelling. The overall performance of the 50 mm thick composites met the requirements of ASTM C578 for expanded polystyrene (EPS), highlighting their potential as viable, bio-based thermal insulation materials.