Transparent plastics coated with a nanonetwork of metal nanowires or carbon nanomaterials are promising future electrodes for large‐area, lightweight, and flexible optoelectronic devices. However, plastics are generally thermal‐ dimensionally instable, meaning that they expand and shrink in response to temperature change. This behavior may severe the ultrathin nanonetwork of the conducting nanomaterials, resulting in reduced performance of the electrodes and resulting optoelectronic devices. Herein, an incredibly thermal‐dimensionally stable (3.26–4.68 ppm K⁻¹) transparent and flexible plastic substrate is presented that results in high thermal performance of the resulting silver nanowire (AgNW) electrode and smart optical device. The high thermal‐dimensional stability is achieved through the generation of a hierarchical network of cellulose nanorods (a highly regarded biobased reinforcing material) in the plastic via a water‐based process. The improved nanocomposite electrode exhibits good electro‐optical performance (12.4–15.6 Ω sq⁻¹ vs 84%); high flexibility; good mechanics even at 150 °C; and the capability to withstand repeated extreme heating and cooling at 150 and −196 °C, respectively. The findings of this study combined with those reported in the literature can show a pathway for further performance improvement of transparent electrodes for future advanced devices.