This work reviews the applications of thermoplastic and thermoset polymers. High-voltage applications of polymer micro/nanocomposites are shown. This study focuses on polyesters, which hold a significant position among polymers as engineering materials used in electronics and electro-technology. Polyester is a widely used and important commercial polymer because of its excellent mechanical, electrical, and thermal qualities. These resins are mixed with other materials to be utilized in high-voltage applications. Consequently, they have found useful applications in the insulation industry for the insulation processing of generators, motors, transformers, and other electrical equipment. Employing micro-nano-sized fillers inside polyester composites has been implemented to enhance their dielectric, thermal, mechanical, and electrical properties and to reduce their flammability. Additionally, this research presents recent enhancements in polyester nano composites using different types of nano fillers and the various applications of Polyester resins used as an insulation material predominantly in super-capacitors, fuel cells, electromagnetic shielding, and textiles. Regarding the medical field, polyester-based materials can be used in hard and soft tissue engineering, wound dressings, surgical implants, vascular, reconstructive surgery, and other medical applications.