The release of solids from a state of shock compression at a free surface is examined. For isentropic release, the postshock specific volumeV′0is shown to be constrained byV′0? (Ufs−Up)2/P1+V1, where (P1,V1) is the pressure‐volume Hugoniot state of shock compression andUfsandUpare the free‐surface and shock particle velocities, respectively. When a sudden phase change occurs during the release process, this lower bound is increased, subject to simplifying assumptions about the phase transition.