Integrally bladed rotors (IBRs) are described. The IBRs include a central hub, an outer rim defining an outer circumference of the central hub, the outer rim defining a plurality of platforms, a plurality of circumferentially distributed blades, wherein a blade extends from each of the plurality of platforms, a rotor slot arranged between two adjacent blades, wherein the rotor slot is defined by a cut within the outer rim, and a rotor slot insert installed within the rotor slot, the rotor slot insert sized and shaped to fit within the rotor slot and prevent air leakage from a first side of the central hub to a second side of the central hub through the rotor slot during operation of the integrally bladed rotor.