This research explores how mushroom mycelium can be integrated with 3D-printed plastic materials to create sustainable biocomposites. Scientists tested whether Fomes fomentarius fungus growing on printed PLA and hemp-reinforced plastic specimens affected their strength and stiffness. Results showed that while pure PLA remained largely unaffected by mycelium growth, hemp-reinforced materials experienced some weakening, with effects depending on the duration of fungal colonization and the internal structure of the printed materials. These findings suggest potential applications in developing eco-friendly building materials and insulation products that combine the benefits of living organisms with manufactured polymers.