Due to its insulating and mechanical properties, mycelium is a promising biomaterial. Nevertheless, its industrial application still faces challenges related to production and surface quality. In order to control the quality of the biocomposite, researchers have studied different substrates. In addition, the importance of sustainability and circular economies is highlighted in the search for alternatives to single-use plastics. This work suggests that these biocomposites can be used to make mycelium molds in which to form biocomposite pieces, reducing the cost of hard tooling, improving sustainable and clean production and disposal. In this work, a series of design recommendations are given for the use of mycelium to make molds and parts.