Rigid polyurethane (PU) foams are widely used for instance in building insulation. Two component systems comprising of a polyol as component A and a diisocyanate as component B are generally applied. Both components are produced from fossil oil resources. The liquid products from fast pyrolysis of biomass contain a large variety of organic compounds with -OH functional groups. This gives rise to the idea to substitute the polyol component in PU foams with such biomass based intermediates. Pyrolysis condensates derived from woody and herbaceous biomass were dried and samples of PU foams were produced with varying amounts of condensate substituting the polyol component. Especially the foams made from condensates produced from straw showed good insulation properties, which were expressed as low thermal conductivity. Here, with a substitution degree of 80% a thermal conductivity of 0.0283 Wm(-1)K(-1) was achieved, which was 8% lower than for the foams produced from commercial components (0.0308 Wm(-1)K(-1)). Preliminary results for the measurement of com-pressive strength indicated that the required value of 150 kPa can easily be achieved, especially with a high degree of substitution. These results show a high potential for the application of bio-based intermediates in the building sector. Further research on other properties is necessary, but the main requirements for thermal conductivity are already met without optimization of the catalyst/stabilizer system.