Foam properties subject to the action of transfer phenomena include thermal conduc tivity (variable gas-phase composition) and dimensional stability (variable total gas pres sure). The commercial importance of such qualities suggests that a detailed analysis of basic mechanisms should contribute to a more rapid advance of rigid foam application tech nologies. Simultaneous consideration of transfer rate theory and material balances produced a model which characterizes the partial pres sures of gases contained within unicellular foams. A supplemental method for systemati cally evaluating resultant unsteady-state nu merical matrices was also developed. A few selected effects of polymers, blowing agents, specimen thickness and surface condition, specimen age, and environmental factors were then discussed and related generally to boards cut from air-filled ( polystyrene) and fluorocarbon-blown ( urethane) foams.