Hygrothermal characterization of bio-based thermal insulation made of fibres from invasive alien lake plants bounded with mycelium

The European program 'Renovation Wave' aims to fasten the energy retrofit of the building stock by increasing by a factor 4 the current renovation rate. Mycelium-based materials gained momentum as insulation solutions in recent years due to their 100% biological composition. However, their durability issues, particularly the risk of fast decay due to high moisture content, need to be investigated to promote a safe use in construction. Two biocomposites were set up at a lab scale, a combination of hemp shives and mycelium and a novel mixture based on the combination of mycelium binder and fibres from a lake plant, Lagarosiphon major, an alien invasive species locally available in many EU internal waters. Samples with different dimensions were used to characterize through experimental tests the thermal conductivity, water absorption (capillarity) and vapor permeability. The results show that these mycelium-based composites present both hydric and thermal properties similar to other biobased material used in construction. The capillarity tests highlighted that hemp composites absorb more water than lake plant ones. The thermal conductivity is similar for both biocomposites, i.e., around 0.05 W/m.K, while the moisture buffer position both analysed biocomposites in “WS 3” according to the German classification DIN 18947 for water regulators.