A process for providing isocyanurate modified methyl diphenyl diisocyanate is provided, the process comprises determine the NCO-value of the MDI; define the NCO-value for MDI; define a ratio of the volume of the MDI to be trimerised over volume of the MDI not to be trimerised; determine, in function of this ratio, the NCO-value of the isocyanurate modified MDI to be provided and the NCO-value of the MDI a target NCO-value for the part of MDI to be trimerised; divide the MDI in two part according to the defined ratio; provide a trimerised part of the MDI by trimerising one of these parts until the target NCO-value is obtained; and terminate the trimerisation by killing the trimerisation catalyst and blend the two parts with each other.