<p>Ag-coated conductive yarns are highly attractive for electronic textiles (E-textiles) such as electrodes and wiring. Nevertheless, their applications are limited by poor surface durability under mechanical stress (e.g., stretching, bending, or rubbing), which compromises the performance. To address this, conductive composite threads were fabricated with polyester yarn (P) and Ag-coated polyamide yarn (AP) with varying fineness (AP70, AP100, AP140, and AP200) under different twisting configurations. In Group #1, with various AP fineness, the threads exhibited improved elongation and enhanced electro-mechanical stability, with 2P-AP140 showing the most balanced properties. In Group #2, with various twisting configurations, while twisting structures were varied. The results indicated that hybrid twisting combining dissimilar fibers (P and AP) led to improved fiber alignment, enhanced modulus, and reduced electrical resistance degradation during repeated stretch-recovery. Among all samples, 2P-AP140 demonstrated the most favorable performance, achieving elongation (33.53 ± 1.47%), and excellent resistance stability (ΔR/R₀ = 4.46 after 1 cycle and 7.61 after the first and 100 cycles, respectively). These outcomes are attributed to optimized filament packing, enhanced inter-filament alignment, and reduced surface roughness. Taken together, these results indicate that conductive yarn fineness and twist configuration are critical structural parameters that determine the mechanical resilience and electrical reliability of composite threads in smart textile applications. Among the fabricated samples, 2P-AP140 demonstrated the most favorable balance of flexibility and stability, making it a strong candidate for wearable technologies such as biometric sensors and flexible interconnects.</p>