The expanding use of polymeric materials for roofing applications requires the development of new accelerated aging test protocols that focus on the degradation mechanisms of polymers. For contractors and consumers to have confidence in new polymeric materials, they must have an understanding of the expected life span of the product. Existing accelerated aging test protocols for underlayments typically have been written for the previous generation of materials. Thus, additional test parameters, which are important in characterizing the performance of polymeric materials, may need to be included in new testing protocols. This work focuses on the use of polymeric materials used in steep slope roofing underlayments. The purpose is to provide a basic background on how polyolefin polymers degrade, how they can be stabilized, as well as the appropriate test methods appropriate for predicting their life span in a roofing environment. Standard accelerated aging test methods are compared to real-time weathering and accelerated aging (thermal). This comparison shows that the current protocols used to determine the durability of polymeric roofing underlayments will need to be updated to consider the temperature of the roof environment.