Statement of the Problem: Light-bodied impression materials with high flow over time are needed to capture preparation margins, particularly with impressions of multiple preparations. Purpose: The flow of five different impression materials (three vinyl polysiloxane, one polyether, and one hybrid) of two setting times (fast and regular) was compared over 30-second intervals. Materials and Methods: Flow was measured using a shark fin testing apparatus (3M ESPE, Seefeld, Germany). A weighted metal caste was suspended above a cup of impression material. The caste was dropped into the impression material, which displaced the material and caused it to flow into a triangular notch within the caste, creating a "shark fin." The test was repeated for each specimen at 30-second increments. These shark fin molds were kept in an incubator to allow setting of the impression materials. After complete setting, the height of the "shark fin" was measured. The data were analyzed using separate two-way analysis of variance and Tukey's HSD post hoc analyses to determine significant intergroup differences (p = 0.05). Results: Shark fin values differed significantly among materials and at each time interval (p = 0.05). Polyether impression materials produced the greatest flow when compared with the vinyl polysiloxane and hybrid materials. Conclusion: Based on the limitations of this study and the materials used, polyether impression material had a better flow profile compared with the vinyl polysiloxane and hybrid materials. © 2011 Wiley Periodicals, 158 Inc.