The rigid polyurethane (PUR) composites with an apparent density of ca. 300 kg/m3 were prepared using 4,4-diphenylmethane di-isocyanate, polyether polyols, an amine catalyst, silicone surfactant and water as a chemical blowing agent. This reference petrochemical formulation was modified with renewable components such as rapeseed oil-based polyols and flax fibers. The effects of the different contents of the two types of the bio-polyols and flax fibers on the mechanical and thermal properties, dimensional stability and water absorption of foamed PUR composites were investigated. The modification showed that the incorporation of bio-components may improve mechanical and thermal properties of final products