The topic of Materials has recently surfaced as a major theme within the research field of interaction design. In this paper we further discuss the need for in-depth descriptions of specific design cases, by revisiting some of our own research-through-design efforts when working with new or not yet fully explored materials for mobile interaction. We outline a series of design challenges that we see commonly arising in this domain, divided into three general themes; 1) affordances of hardware and casings, 2) experiential properties of different software solution, and 3) material properties of sensors, radio-signals, and electricity. Our main conclusion is that research in interaction design needs an extended focus on how systems are crafted from and together with properties of digital materials, and how new knowledge gained from those processes can be shared.