The search to lighten material is a major trend accompanying the development of several sports and recreational mountain practices (ski touring, trail running, fast hiking, etc). Such characteristics as lightness, technicality, and durability are not easy to combine for the designers. Two emblematic inventions of this successful equation have drawn our attention (a climbing harness, and a backpack). We undertook a sociological analysis of these innovatory trajectories: in a socio-technical perspective, 15 semi-directive interviews have been conducted with partakers of the two innovations. Our results point out the complexity and unpredictability of such processes. These inventions are approved in the restricted circle of experienced outdoor professionals and practitioners; but in spite of this recognition, their attaining the status of innovation can be subject to debate, because of limited compromises, little broadening of the network, and a clear turn towards restrictive practices.