Rigid polyurethane (PUR) foams with the apparent density in the range of 45—60 kg/m3 were produced from tall oil polyol (TOP) and organosolv wheat straw lignin as filler. PUR foams were filled with lignin in the amount of 0—6.3 wt %. Mechanical properties, dimensional stability, water absorption and thermal conductivity of prepared foamswere investigated. The use of lignin increased the content of renewable materials in the end product, reaching together with TOP the value of 23.6 wt %. The viscosity of polyol system and foaming process parameters (cream time, gel time, tack-free time and full rise time) were determined. The viscosity of polyol system rose exponentially when concentration of lignin in the PUR foam was increased. The maximum value of compressive strength (0.35 MPa parallel to the foaming direction) was reached in two PURsamples where the concentration of lignin in foam was 1.2 wt %. It was concluded that wheat straw lignin can be used as a filler to obtain rigid PUR foams having the characteristics of thermal insulation material.