BACKGROUND: To compare the water absorption of 12 FDA-approved hyaluronic acid (HA) facial fillers in vitro in conditions relevant to in vivo injection. OBJECTIVE: The goal of this study was to provide long-term insight into an improved, tailored facial rejuvenation approach and to understand sequelae that could affect preoperative surgical planning. METHODS: In 2 experiments, 12 FDA-approved HA fillers were loaded into test tubes with nonpreserved normal saline and then placed in a 94.5°F-96°F environment for 1 month to allow water absorption by passive diffusion. The test tubes were centrifuged so that the hydrated filler could pass to the bottom of the tube. The tubes were centrifuged for 12 minutes at 1,200 revolutions per minute in the first experiment and for 7 minutes in the second experiment. A blue dye was then instilled to demarcate the filler/saline interface. RESULTS: There was variation in the water absorption of different HAs. Low absorption occurred in non-animal-stabilized hyaluronic acid. CONCLUSION: The pattern of water absorption was similar in the 2 experiments. The results inform us about in vivo conditions and provide guidance for filler selection.