In this study, an alternative biobased matrix is proposed to replace synthetic fibres or mineral binders that are used as binders between plant particles in insulation materials. This binder is produced from mycelium, the filamentous vegetative part of fungi, and allows the manufacture of 100% biobased mycocomposites. This article presents the results obtained with regard to the optimization of the formulation and processing conditions of mycocomposites. The materials were obtained from Pleurotus ostreatus and hemp aggregates. The impact of the plant/mycelium ratio, the addition of a catalyst and the particle size is evaluated on the density, thermal conductivity and mechanical strength of the mycocomposites obtained. The results show that it is possible to obtain 100% biobased insulating building materials with a density between 115 and 150 kg/m 3. Their thermal performance is comparable to that of traditional insulating materials, i.e. around 50 mW/(m.K)-1. Their compressive strength is low and mycocomposites have high elongations at break. In addition to this work, the durability of these mycocomposites and their endof-life, recycling or biodegradation, will also be studied in order to obtain an overall assessment of the environmental impact of the materials.