An analytic model is developed to describe the final state reached by a gas‐filled spherical shell compressed by a constant ablation pressure. The model takes into account the solid compressibility and the mass loss by ablation, and gives the magnitudes that characterize the state of the gas and solid when the implosion stagnates. The model provides an adequate physics interpretation and an extension of a recently reported model [B. Ahlborn, M. H. Key, and A. R. Bell, Phys. Fluids25, 541 (1982)]. The restrictions of the model imposed by the approximations adopted are discussed. The results are compared with available numerical simulation data and with the previous model already mentioned, and the main differences between them are discussed.