The article compares the properties of bio-polyols obtained from white mustard (Sinapis alba) seed oil, which contain boron and sulfur atoms. Each of the bio-polyols was prepared by a different method of testing the efficiency of the incorporation of boron and sulfur atoms. All synthesis methods were based on the epoxidation of unsaturated bonds followed by the opening of epoxy rings by compounds containing heteroatoms. Two of the bio-polyols were subjected to additional esterification reactions of hydroxyl groups with boric acid or its ester. Three new bio-polyols were obtained as a result of the performed syntheses. The synthesized compounds were subjected to detailed physicochemical (physical state, color, smell, density, viscosity and pH), analytical (hydroxyl number, acid number, water content, content of C, H, N, S, O, B elements and GPC analysis), spectroscopic (FTIR,1H NMR and13C NMR) and thermal (DSC) tests. The obtained results allowed for a detailed characterization of the synthesized bio-polyol raw materials. Their suitability for obtaining polyurethane materials was also determined. The synthesized compounds have been found to be an interesting alternative to petrochemical polyols. The influence of the synthesized compounds on the flammability of polyurethane materials was tested experimentally. On the basis of this testing, a number of rigid polyurethane/polyisocyanurate foams were obtained, which were then subjected to flammability tests with the methods of horizontal and vertical burning, limiting oxygen index (LOI) and using the cone calorimeter. Based on this research, it was found that the presence of sulfur and boron heteroatoms reduced the flammability of polyurethane materials based on synthesized bio-polyols.