The shock compression and unloading of several simple homogenous binary mechanical mixtures with polyethylene as the matrix is compared to that of an aluminum fiber/epoxy matrix composite. When both of these systems are unloaded from shock states lying in the liquid regime for the matrix, the latter physically separates from the rigid component and exhibits independent motion. The measured free‐surface velocity is that of the matrix material and is predicted by an internally adiabatic compression/isentropic expansion model.