This paper examines the use of free volume approaches to describe the gel effect in free radical polymerization, specifically testing the consistency of free volume in describing the effect of temperature on the critical onset conversion for the gel effect, X-crit. Experimental polymerization results for both methyl methacrylate (MMA) and styrene in which the temperature, T, is varied while the molecular weight, M, is held nearly constant show that the critical onset conversion for the gel effect, X-crit, is affected by T; i.e., a higher T leads to a higher X-crit, consistent with free volume. Other studies purported to show a link between X-crit and M did not account for variations in T in the data analyzed, and it is highly likely that part of the X-crit trend reported to be caused by M was in fact related to T variations. Further examination of this issue via modeling indicates that the experimental results are consistent with the quantitative trend predicted by free volume for X-crit as a function of T as well, indicating that free volume is an appropriate basis for modeling the gel effect as it adequately handles effects of temperature on termination. However, as it does not describe the concentration or potential molecular weight dependence of termination, free volume is not a complete theory for the gel effect. For this task, additional molecular-level insight is needed, a fact underscored by certain experimental trends not predicted by free volume, such as the effects of chain transfer and solvent quality on termination.