Intumescent coating composition comprising a polyisocyanate, a polyfunctional isocyanate-reactive compound and an intumescent ingredient, wherein the intumescent ingredient contains at least one or more compounds containing phosphorus, nitrogen and boron atoms and the weight ratio phosphorus to nitrogen in said intumescent ingredient is between 0.5/1 to 1.5/1 and the amount of boron is from 1 to 5 wt % based on the coating composition.
