Two rapeseed-oil-based polyols were synthesized by partial epoxidation of the double bonds in fatty acid chains and overall opening oxirane rings by using diethylene glycol. Flexible polyurethane foams with varied isocyanate index and modified by partial substitution of petrochemical polyether triol with rapeseed-oil-derived polyols were obtained. Bio-polyols: Polyol I and Polyol II differed in functionalities (2.5 and 5.2, respectively) and hydroxyl values (114 and 196 mg KOH/g, respectively). Influence of the bio-polyols on mechanical properties, resilience, apparent density, and cellular structure of synthesized foams was investigated. Compression properties were examined and compared via determining compression values and compression stressstrain characteristics, as well as tensile strength and elongation at break were estimated. Foams modified with Polyol I had higher values of resilience and elongation at break than those with Polyol II, while higher tensile and compression strength and superior cell structure were observed in the case of foams modified with Polyol II. (C) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012