A central tenet of HCI is that technology should be user-centric, with designs being based around social science findings about users. Nevertheless a repeated but critical challenge in design is translating empirical findings into actionable ideas that inform design, or generating implications for design. Despite various design methods aiming to bridge this gap, knowledge informing design is still seen as problematic. However there has been little empirical exploration into what design researchers understand by such design knowledge, the functions and principles behind their creation. We report on interviews with twelve expert HCI design researchers probing the roles and types of design implications, and the process of generating and evaluating them. We synthesize different types of design implications into a framework to guide their generation. Our findings identify a broader range than previously described, additional sources and heuristics supporting their development as well some important evaluation criteria. We discuss the value of these findings for interaction design research.