Urethane prepolymers with terminal isocyanate groups, obtained from a toluene diisocyanate (TDI) and selected polyols, can be adopted for chemical modification of unsaturated polyester resins. Optimal amounts of urethane prepolymer modifiers are a to 7 weight parts of a resin. This assures the composite hardness and makes possible its processing. Modified polyester-urethane compositions shows enhanced impact resistance and lesser hardness in comparison with unmodified polyester resin. They can be applied to manufacturing of the glass reinforced mat laminates, because greatly enhances their tensile strength and lenghthens the relative cracking elongation.