Sustainable Insulation Panels Made of Tree Bark Fibers: Thermal and Fire Performance

The growing demand for sustainable solutions stimulates the building sector to develop environmentally friendly building materials. However, innovative natural-based options used in residential buildings must also comply with safety standards. This study examines the thermal and fire performance of insulation boards produced from tree bark fibers of two hardwood species, Tilia spp. (Lime) and Robinia pseudoacacia (Black Locust). The samples were fabricated using a wet process without adhesives and fire retardants, achieving thermal conductivity coefficient values of 0.055–0.057 W/m·K at densities ranging from 218 to 231 kg/m3. Density profiling revealed a characteristic vertical gradient associated with wet processing, while wettability measurements indicated hydrophobic surface behavior. Fire tests showed species-dependent behavior: Black Locust panels exhibited smaller damaged zones and lower maximum temperatures, whereas Lime panels showed deeper thermal degradation. No board ignition was observed, and smoke release remained moderate and consistent. Overall, these findings highlight the potential of bark-based insulation boards as sustainable alternatives in building applications. However, further optimization with larger sample sets and the integration of natural flame retardants is recommended to improve performance and safety.