In order to further our understanding of polymer durability, the degradation kinetics of a series of polymers was studied. The Arrhenius activation energy was used as the parameter to follow the rate dependence as a function of temperature. For most systems, it was evident that the apparent activation energies increase monotonically with temperature. This finding explains the frequent observation that kinetic parameters obtained at high temperatures often lead to grossly optimistic estimates of shelf life at ambient conditions. The activation energies of polypropylene from the surface embrittlement processes were also found to have a striking similarity to the thermal processes, with nearly identical activation energies at the same temperature. A good understanding of this observation could lead to broader applications and further the understanding of polymer degradation.