Mycelium composites is a new class of renewable materials which can be used for heat insulation of buildings. Use of the composites would help to reduce both operational energy consumption and embodied energy of building insulation materials. In addition, use of the renewable composites could also reduce embodied greenhouse gas (GHG) emissions of the insulation materials. Local production and use of the composites could stimulate residential building insulation process via additional socio-economic benefits, such as positive impact on local economy, created workplaces and reduced import. The research question of this study is to determine a difference between embodied energy and GHG emissions of the mycelium insulation material and synthetic insulation alternatives. System dynamics model is used as the method for assessment of the dynamics of the total embodied energy and GHG emissions if equal amounts of the insulation materials is produced. Time horizon for the modeling is 2021–2050. Data used in the model were taken from scientific publications and laboratory experiments with growth process and properties of the mycelium composites. The model includes several feedback effects, e.g., effect of research and development on efficiency and productivity of the mycelium production process. The results show that embodied energy of the mycelium insulation material is higher than for the synthetic alternatives but the embodied GHG emissions are considerably lower than for the alternatives. The embodied GHG emissions are even lower if the absorption of CO2 of renewable materials used for the production of the mycelium composites is included.