ABSTRACT Wood fiber insulation boards (WFIB) produced with natural binders have been gaining recognition as an eco-friendly material, however there is limited information on the effect of different wood fiber and sustainable binders on WFIB production. This study investigates the impact of density, wood fiber origin, and pertinency of polylactic acid (PLA) as a binder. Flexible WFIB with densities of 80, 100 and 120 kg/m3 were produced by hot-press method with fibers of pine and spruce as softwoods, and beech and birch as hardwoods. Bicomponent fibers, composed by two concentrical layers of polylactic acid (PLA) were utilized as a renewable-origin binder at a proportion of 10%. Technological properties such as short-term water absorption, compression test and thermal tests properties were assessed. The density of the WFIB significantly influences the water absorption, compression strength, and thermal conductivity, with all these values increasing as the density rises. Insulation boards made from hardwood fibers showed greater water absorption and compression values compared than their softwood counterparts. Softwood-WFIB single-samples with a density of 80 kg/m3 reported lower thermal conductivities than hardwoods ones. The present study shows the promising feasibility of producing flexible wood fiber insulation boards from natural fibers and polylactic acid as a renewable binder.