This study presents a method to enhance the thermoelectric performance and flexibility of PEDOT:PSS fiber bundles through a combination of wet-spinning and rational post-treatment with concentrated sulfuric acid. The fibers are doped with dimethyl sulfoxide (DMSO) to improve their spinnability and conductivity. After post-treatment with 98% sulfuric acid, the fibers exhibit significantly increased electrical conductivity (up to 4464 S cm⁻¹) and a power factor of 80.8 μW m⁻¹ K⁻², which is highly competitive compared to previously published studies. The fiber bundles also demonstrate high mechanical strength and flexibility, making them suitable for wearable thermoelectric applications. The thermoelectric device based on these fibers can generate a power output of 2.25 nW at a temperature difference of 25 K. The study highlights the potential of all-organic, flexible, and highly conductive textiles for energy harvesting and wearable electronics. The results suggest that the developed fiber bundles can be used in various applications due to their high thermoelectric performance and flexibility. The research provides insights into the fabrication of flexible, high-conductivity, and thermoelectric textiles.This study presents a method to enhance the thermoelectric performance and flexibility of PEDOT:PSS fiber bundles through a combination of wet-spinning and rational post-treatment with concentrated sulfuric acid. The fibers are doped with dimethyl sulfoxide (DMSO) to improve their spinnability and conductivity. After post-treatment with 98% sulfuric acid, the fibers exhibit significantly increased electrical conductivity (up to 4464 S cm⁻¹) and a power factor of 80.8 μW m⁻¹ K⁻², which is highly competitive compared to previously published studies. The fiber bundles also demonstrate high mechanical strength and flexibility, making them suitable for wearable thermoelectric applications. The thermoelectric device based on these fibers can generate a power output of 2.25 nW at a temperature difference of 25 K. The study highlights the potential of all-organic, flexible, and highly conductive textiles for energy harvesting and wearable electronics. The results suggest that the developed fiber bundles can be used in various applications due to their high thermoelectric performance and flexibility. The research provides insights into the fabrication of flexible, high-conductivity, and thermoelectric textiles.