Transport of air (with solvent vapor) bubbles that sometimes appear in a polymer/solvent liquid are followed in the process of solvent casting the polymer. The concentration profile of the solvent in the developing casting is found to be the primary controller of bubble rise velocity, This velocity dependence on concentration is developed through experiment over the range of conditions in the casting [similar to 90 to 0% methylene chloride in poly(methyl methacrylate), molecular weight 300,000, and Tg 110 degrees C]. Assumptions of quasi steady-stale and penetration type theories are used to generate this simplest model, qualitatively (and semi-quantitatively) correct in predicting the skin layer/bubble layer/bulk layer structure in solid polymer pieces produced by the solvent casting process.