Background: The second-generation peripheral hydrogel coils were recently introduced. However, it remains unclear how effectively these coil packs compare to fibered and bare coils, and whether they are prone to hydrogel dislodgment. The purpose of this study was to compare the packing densities of second-generation peripheral hydrogel coils with fibered and bare coils and to determine their susceptibility to hydrogel dislodgment. Methods: Twelve second-generation peripheral hydrogel coils, 12 fibered coils, and 12 bare coils were each inserted into a flow model under fluoroscopy. Each type included three coils of 0.018-inch with 4-mm and 6-mm diameters, and three of 0.035-inch with 6-mm and 8-mm diameters. Packing densities were calculated and compared for each specification. Additionally, hydrogel dislodgment in the flow model was analyzed over a 28-day period. Results: Bare coils demonstrated significantly higher packing densities compared to hydrogel coils (0.018-inch 4-mm: P=0.013; 0.018-inch 6-mm: P=0.009; 0.035-inch 6-mm: P=0.013; 0.035-inch 8-mm: P<0.001) and fibered coils (0.018-inch 4-mm: P=0.005; 0.018-inch 6-mm: P=0.015; 0.035-inch 6-mm: P=0.028; 0.035-inch 8-mm: P<0.001). Hydrogel coils did not significantly differ from fibered coils (0.018-inch 4-mm: P=0.627; 0.018-inch 6-mm: P=0.859; 0.035-inch 6-mm: P=0.070), except for the 0.035-inch 6-mm coils, where their packing density was significantly lower (P=0.006). Over 28 days, 206.7±45.1 hydrogel fragments dislodged from the 0.018-inch 4-mm coils, 178.7±37.1 from the 0.018-inch 6-mm coils, 211.0±27.1 from the 0.035-inch 6-mm coils, and 211.0±27.1 from the 0.035-inch 8-mm coils. Conclusions: Second-generation peripheral hydrogel coils did not demonstrate superior packing densities compared to fibered and bare coils and may be susceptible to hydrogel dislodgment.