The intensity upgrade of ISOLDE will make beams of even more exotic isotopes feasible, given that the isotope of interest can be separated from contamination. Beam purity is crucial for a range of physics cases, including many reaction studies that will be possible at HIE-ISOLDE. The HRS upgrade aims at achieving a mass resolution R » 20 000. In my talk I will present the chosen HRS design, implications for physics and the current status of the project.