Polyvinyl chloride (PVC) rheology is greatly influenced by its low crystallinity content and its particulate morphology. The present paper will discuss the role of morphology in the flow behavior of rigid PVC in both constrained and unconstrained recoil. PVC has a partially fused structure and the fusion level can be monitored with surface electron micrographs of the fracture surface. When PVC is suddenly (step) elongated, the fusion level is greater than in the unstrained state and increases with time. The relaxation behavior is close to a power-law function with a Doi-Edwards type damping function. In constrained recoil (reversing double step elongations) the fusion level is still greater than in the unstrained state and Wagner’s irreversible model fits the data. In unconstrained recoil (step elongation followed by stress removal) it is shown that the fusion level almost returns to its initial state. In order to predict this unexpected change, we use a modified Wagner irreversible model with a structural parameter affecting the relaxation behavior.