Increased CO₂ fixation and reduced embodied energy of mycelium bio-composite materials grown on a mixed substrate over diurnal temperature cycles

There is a pressing need for alternative construction materials that can facilitate the transition to a sustainable circular economy. Mycelium-based bio-composites are an example of such materials. They have a low embodied energy compared to concrete-based materials and commercial thermal insulators, and act as a net CO₂ sink. So far, mycelium materials have been produced using homogenous substrates and by growing at a fixed temperature. Growth at a fixed temperature accounts for 73% of the embodied energy and more than 40% of the CO₂ emissions. Here, mycelium bio-composites were grown using temperature cycles mimicking ambient temperature conditions during an Israeli transition season or a summer day in the Netherlands without impacting material qualities or time of production. These results verify a possible strategy to dramatically reduce energetic and CO₂ cost of mycelium materials fabrication, and the findings imply that monolithic structures can be grown in situ at outdoor construction sites. The use of mixed substrates allows a wide range of final properties that can be tuned by the composition. Also, thermal conductivity values as low as 0.026 W m⁻¹ K⁻¹ were obtained by growing the mycelium bio-composite on mixed or homogenous substrates. These results show that mycelium materials with superior thermal insulation properties can be grown at ambient temperature using mixed as well as homogenous waste streams.