Flexible polyurethane foams made of a corn. polyol and toluenediisocyanate were modified by the addn. of ZnBO3, melamine cyanurate, expandable graphite and red P flame retardants (15% by mass) and studied for apparent d., flexibility, linear flammability, O-2 index and thermogravimetric anal. The addn. of flame retardants resulted in an increase in apparent d. and thermal stability and in a decrease in mech. strength of the foams. Only addn. of the expandable graphite and red P resulted in an increase in the O-2 index.