The present work focuses on the study of the theological behavior in extension of three different polystyrene melts (a general-purpose polystyrene, GPPS, a high-impact polystyrene, HIPS, and a 50/50 blend of both), in particular the behavior at failure and at rupture in extension that are (ultimately) related with the materials' ability to endure the various stages of extension-dominated processing sequences such as thermoforming. The aim Is to try to explore possible synergistic effects arising in extension-dominated flows by means of physically blending the two base materials. The rheological characterization was performed in terms of both the linear and non-linear viscoelastic behavior, in shear and extensional flows. The results show that blending the two materials has important consequences on the extensional behavior, the blend showing a higher degree of extension-thickening than either GPPS or HIPS and that there is indeed a synergistic effect in what regards the rupture and failure behavior.