abstract The building sector accounts for high energy consumption, and increasing the energy efficiency of buildings is considered a key measure to meet the climate goals worldwide. Even though there are various residual biomass streams available that show good thermal insulation properties, most applied thermal insulation materials are of mineral or synthetic polymer basis and non-biodegradable. To foster the application of bio-based thermal insulation materials, the aim of this study was an investigation of bio-composite- and mycelium-based boards and mats currently available or under research and their thermal insulation properties. The focus was laid on the treatment of various biomasses using fungi to enhance their application in the building sector as well as their thermal insulation properties. The different materials were compared regarding density, thermal conductivity, specific heat capacity, water vapour resistance, water absorption, fire performance, and mechanical properties. This work provides the basis for selecting residual biomass streams to produce case-specific thermal insulation materials.