A condensed review will be presented regarding the bubble growth study. A modified model fitting to foam extrusion system will be discussed. The improved model focuses on the influence of blowing agent on bubble growth during thermoplastic foam extrusion. Extrusion has been conventionally used for producing low-density foam sheet and rods with physical blowing agents in the last decades. Foam nucleation, bubble growth, and cell coalescence are the three major events in the foaming process. Only the bubble growth study is addressed here. The bubble growth is influenced by the concentration-dependent blowing agent diffusion coefficient, transient cooling of the expanding foam, influence of blowing agent on polymer viscosity, and the escape of blowing agent from the surface of the foam. The blowing efficiency is affected by the escape of gas from the cells closer to the surface of the foam. Previous models in the literature do not consider these significant influences. A modified model will be presented accounting for those more subtle effects. In addition, a new experimental technique will be described to collect experimental bubble growth data. Predictions of the new model reasonably agree with the experimental data.