Calculations of high‐explosive (HE) driven plasma opening switches have been extended to two dimensions. The goal of our calculations is to determine the role of mixing in the resistance increases that are observed experimentally. We have not included a magnetic field, but have looked at the hydrodynamics of the interface between the cool HE detonation products and the hot plasma. Our calculations indicate that significant mixing can occur if perturbations exist along the interface. We estimate the sensitivity of our results to the wavelength and amplitude of these perturbations.