## 3 Results and Discussion  
### Characterization of the Mycelium-Based Composites  
HERF, SDLS, WS, and PS were chosen as substrates for this study primarily because of their widespread availability globally, particularly in Bulgaria, where they are significant by-products of the essential oil and agricultural industries. Despite their potential value, waste plant biomass is often overlooked and discarded. _G. resinceum_ GA1M, isolated from Bulgaria, demonstrates favorable growth kinetics when colonizing various lignocellulosic substrates, resulting in the formation of MBCs. Visually, all obtained mycelium composites exhibited a surface texture that could be characterized as smooth and velvety to the touch and have good dimensional stability (Figure 2). Figure 2: MBC’s samples (**A**) (HERF), (**B**) (SDLS), (**C**) (WS), (**D**) (HERF:WS), (**E**) (SDLS:WS), (**F**) (WS:PS). The complete coverage of the composite by aerial mycelium and the dense network of hyphae in the material's center significantly affect its physical and mechanical properties. An increased closed (not accessible to water) porosity of MBCs was targeted in order to achieve lower density and thermal conductivity than in our previous study [11], while ensuring minimum compressive strength and keeping water absorption within certain limits. In order to be able to compare the physical and mechanical characteristics of MBCs with those of thermal insulating products for building applications, the characterization methodology applied was based on standardized methods, adapted to the MBC samples' peculiarities (shape, size, number). There were structural differences between the core and the near-surface zones of the samples, due to the mycelium \"coating\" of the near-surface zones. The testing was performed on intact samples because the removal of the coating (e.g., by cutting or sawing) might lead to different types of degradation of different MBCs. Thus, the results reflected the overall behavior but were highly influenced by the surface/volume ratio. In case the bio-composites are to be used in applications where the edges need to be trimmed or the surface layer removed, the tests must be carried out on the relevant representative samples. The results from the testing of the physical and mechanical properties of MBCs are summarized in Table 1.  
The apparent density of the studied MBCs varies between 110 and 250 kg/m\({}^{3}\), thus being close to many thermal insulating materials used in buildings, such as rigid and semi-rigid mineral wool boards, foam glass, mineral insulation boards, etc. Compared to conventional thermal insulating materials, such as EPS, XPS, PUR, or PIR, having densities from 15 to 50 kg/m\({}^{3}\), the apparent density of MBCs is higher [10; 33; 52; 53; 54]. However, the mycelium-based binder seems to be a much more efficient binder in terms of thermal insulation than other binders, usually used with natural particles such as lime, gypsum, and cement (e.g., in particle boards, hempcrete, etc. ), because the pure mycelium itself has very low density of 0.03-0.05 g/cm\({}^{3}\)[14]. The thermal conductivity of all studied MBCs characterizes them as very efficient, being below 0.06 W/mK, while the \(\lambda\)-value of the composites mentioned above is usually in the range of 0.06-0.12 W/mK, indicating thermal insulating materials with medium efficiency. The presented results on thermal conductivity correlate very well with the forecasts made in our previous study [11], those reported by [PERSON] et al. [43], and [PERSON] et al. [29]. They also show a good relationship with the apparent density of MBCs, just as with the majority of thermal insulating materials--Figure 3. The lower apparent density of  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{ \begin{tabular}{c} **MBCs** \\ **Application** \\ **Density,** \\ **\(\rho_{\mathbf{a}}\)** \\ \end{tabular}  } & \begin{tabular}{c} **Compressive** \\ **Resistance at 10\%** \\ **Deformation,** \\ **\(\sigma_{\mathbf{10}}\)** \\ \end{tabular}  &