Rapeseed oil was transesterified with triethanolamine or transamidized with diethanolamine at 170 degrees C or 140 degrees C, resp., in presence of Zn(OAc)(2) catalyst or epoxidized with H2O2 in AcOH/H2SO4 and converted to bio-polyols by opening oxirane rings with diethylene glycol in presence of H2SO4 at 95-100 degrees C. The bio-polyols (hydroxyl no. 270-390 mg KOH/g) were used for partial replacing a polyol of petrochem. origin (70% by mass) in prodn. of rigid polyurethane-polyisocyanurate foams in reaction with polymeric diphenylmethane-4,4'-diisocyanate to study the foaming course. The mech. properties, cellular structure and thermal cond. of the foams were detd.