Mycelium composites are intended to replace plastics in different applications as lightweight, sustainable alternatives. One major limitation is the exchange of oxygen and heat in the core of the material. Bio-welding allows the stacking of thinner layers that are then connected by fungal mycelium. We screened six different fungi for their growth rate, binding strength and gap-bridging capability before fabricating bio-welded composites from beech sawdust with two of the fungi, using two different particle sizes and growth durations. The influence of these parameters, as well as the number of layers and their orientation in the material, on internal bond strength and thermal conductivity was assessed. We found that the maximum gap-bridging distance of a fungus is less essential than the strength of the mycelium connection. Most importantly, the surface roughness of the layers must be minimized to ensure that the bio-welded interface is stronger than the individual layers.
