Building and construction waste contributes to global carbon emissions, leading to the need to seek alternative materials that are more environmentally friendly. Mycelium Biocomposite (MB) is a sustainable material that utilizes agricultural waste as its main substrate and can be degraded after-use. This study aimed to investigate mechanical performance of additional layers in sandwich panel fabrication of MB. The experiment was conducted in two phases including (1) Composite 1: Oil Palm Empty Fruit Bunch (OPEFB) fiber layer with pine resin and (2) Composite 2: MB sandwich panel. In Composite 1, the mechanical test results showed the S50 sample (50 % fiber and 50 % resin) had the highest tensile strength of 0.18 N/mm² and was selected as the surface layer. In Composite 2, the variable of layer binder was produced using mycelium hyphae (MB-M) and resin (MB-R). The results of the physical, mechanical, and thermal properties tests were compared with the JIS A 5905:2003 standard and previous studies. The MB sample (no layer) had the best mechanical and thermal conductivity values due to the binding method effects, such as flexural strength at 25.38 N/mm² and bending strength at 0.53 N/mm². MB-M showed incomplete drying that caused lower tensile strength and higher thermal conductivity. Meanwhile, MB-R showed mechanical values similar to MB, such as flexural strength at 21.22 N/mm² and bending strength at 0.52 N/mm². Yet, MB had higher thermal conductivity, where MB-R showed 0.1558 W/mK and MB showed 0.1037 W/mK, due to Composite 1 addition. This study suggests the development of MB thermal values and considers its application as non-structural insulation panels. © 2024 Elsevier Ltd