Achieving adequate wall apposition is a crucial technical goal when deploying flow diverters to treat wide-neck cerebral aneurysms. The socalled J-wiring technique is a common method used to optimize flow diverter wall apposition. However, the frictional interaction between the shaping device and the microguidewire tip during the formation of the J-loop, as well as the interaction between the J-loop and the flow diverter during J-wiring, may potentially cause damage to the guidewire’s coating. Three frequently used guidewires were tested in vitro in a silicone aneurysm model. Manual J-shaping of guidewire tips, along with the J-wiring technique (including J-shaping), caused damage to the surface coating of guidewires, as observed by scanning electron microscopy. Therefore, both mechanisms may contribute to the generation of polymer micro-fragments in patients treated with flow diversion.