With the growth of optogenetic research, the demand for optical probes tailored to specific applications is ever rising. Specifically, for applications like the coiled cochlea of the inner ear, where planar, stiff and non‐conformable probes can hardly be used, transitioning from commonly used stiff glass fibers to flexible probes is required, especially for long‐term use. Following this demand, Polydimethylsiloxane (PDMS) with its lower Young's modulus compared to glass fibers could serve as material of choice. Hence, we investigated the long‐term usability of PDMS as a waveguide material with respect to variations in transmission and refractive index over time. Different manufacturing methods for PDMS‐based flexible waveguides were established and compared with the aim to minimize optical losses and thus maximize optical output power. Finally, the waveguides with lowest optical losses (−4.8 dB/cm ± 1.3 dB/cm at 472 nm) were successfully inserted into the optogenetically modified cochlea of a Mongolian gerbil (meriones unguiculatus), where optical stimuli delivered by the waveguides evoked robust neuronal responses in the auditory pathway.This article is protected by copyright. All rights reserved