The need for electronics that is compatible with life is driving the search for electronically active materials that may be used for transferring integrated circuits onto flexible substrates. One route is to build transistors, which modulate the conductivity of organic thin films with a lateral gate. However, as is well known in the case of graphene, the in-plane conductivity cannot easily be switched off. Another route is to use negative differential resistance (NDR) phenomena. Until recently, NDR was only obtained from band engineered semiconductors. This article reviews the recent development of flexible materials that specifically make use of transport perpendicular to graphite planes to obtain NDR. These materials include h-boron-nitride/graphene multilayers and graphite-silicone composites. We report on the dependence of their current-voltage curves on deformation, changes in structural and experimental parameters. We also describe device implementations in the form of flexible oscillators, amplifiers and memories.