Safety is a top priority and daily concern for roofing contractors. The purpose of this study was to provide an understanding of the physical properties that affect the safety characteristics of roofing underlayments. This was done in a three-step process by defining levels of safety performance with respect to grip and traction, identifying the mechanical properties of underlayments that enhance performance, and developing and confirming the scientific explanation for the efficacy of these mechanisms. In residential roofing, there are several grades of roofing felt and dozens of brands of synthetic roofing underlayments, each offering some type of safety feature in the areas of traction and grip, also known as “walkability.” The challenge has been the lack of a measurement system that accurately translates the physical properties of underlayments into walkability. In order to meet this challenge, this study started with the concept of walkability by having roofing contractors rate and rank various types of underlayment materials in terms of walkability. This evaluation included the grip of the underlayment to the deck and the grip of the contractor's footing to the underlayment. Because roofing installers work under different environmental conditions, the scope of the walkability evaluation process included conditions where the test deck and materials were wet or dry, as well as under warm and cold conditions. In the rating and ranking of these products by roofing contractors, it was found that the performance of some products increased at lower temperatures, while the performance of other products was diminished at lower temperatures. It was also found that some underlayment materials maintained a good level of walkability under wet and dry conditions, while other materials did not. Thus, the measurement systems developed to characterize these products considered all conditions, as well as correlated them to the input provided by the contractors.