This chapter focuses on the main environment of thin films: the substrate. The last two chapters have studied the films that allow these neuromorphic devices to operate. Generally, most thin film devices have a substrate on which the film is situated. Without these substrates, many of the interesting properties of thin films would not come about. Typically, only the films are studied to understand how they respond to different substrates and external perturbations. As such, it is assumed that these substrates remain inert and rigid, only there to provide support for the film. However, this is not the case for these neuromorphic systems which can change their underlying substrate and, in turn, feed back into the film affecting its properties.