<p>The presented research concerns the synthesis of rigid polyurethane/polyisocyanurate foams using three bio-polyols based on white mustard seed (<i>Sinapis alba</i>) oil, which contain different content of sulfur heteroatoms and examining its impact on the basic physico-mechanical properties, flammability and smoke emission of these materials. The research included testing of performance parameters such as apparent density, compressive strength, brittleness, absorbability, water absorption and thermal conductivity coefficient λ. The test method using a cone calorimeter according to ISO5660:2015 standard was used to determine fire and smoke-emission properties. During one test, the following parameters were determined: time to ignition, heat release rate, maximum average rate of heat emission, total heat released per unit area of the analyzed material, effective heat of combustion, mass loss rate, mass lost, total smoke production, gas release rate (CO, CO₂), total smoke release. The obtained results showed that the share of bio-polyols in the formulation had a significant influence on the physico-mechanical properties of the obtained foams. Moreover, analysis of fire and smoke-emission properties using the cone calorimeter method confirmed that materials based on bio-polyols posed a lower fire risk than the reference material based on commercial raw materials. Moreover, it was found that the increase in the amount of sulfur heteroatoms in the material significantly contributes to the reduction of all parameters related to the flammability of foams. However, it also affects the increase in carbon monoxide and carbon dioxide emissions during the combustion process.</p>