This paper presents an innovative fungal mycelium-based biofoam. Three different mixing protocols with various substrate materials, including wood pulp, millet grain, wheat bran, a natural fiber, and calcium sulfate, and two packing conditions were tested to produce samples for physical, thermal, and mechanical property characterization. Dry density, thermal conductivity, elastic moduli, Poisson’s ratio, and compressive strength were obtained. It was found that densely packed samples following Mixing Protocol II have the highest dry density, elastic moduli, compressive strength, and comparable thermal conductivity, and have met or exceeded like characteristics of the conventional polymeric thermal foams except dry density. The results demonstrate that this biofoam offers great potential for application as an alternative insulation material for building and infrastructure construction, particularly in cold regions, or as light-weight backfill material for geoengineering applications.