There has been speculation that the macroscopic properties of foams, such as air flow, are directly related to foam compression set. However, it has since been recognized that the molecular structure is the relevant size scale for understanding the compression sets, which are simply symptomatic of the underlying polymer structure resulting from the polymerization reactions that occur during foaming (Sonnenschein et al. 2007). Researchers have empirically determined that formulation modifications can result in large differences in compression set values