The sportswear industry has experienced substantial growth, propelled by increasing consumer awareness of healthy lifestyles and the convergence of fitness and fashion. This study quantitatively evaluates the impact of three stitch types (knit, tuck, and miss) in weft-knitted fabrics produced from double-ply polyester yarn on key thermal comfort and functional properties of sportswear. Physical characteristics (thickness and weight), air permeability, abrasion and pilling resistance, moisture absorption (water drop test), and moisture management of these structures were systematically evaluated. Results demonstrated that the fabric containing tuck stitches exhibited superior performance, with the highest air permeability (122 cm³/cm²/s), fastest moisture absorption (15 seconds), and favorable pilling resistance (9 pills/cm² after 2000 abrasion cycles), showing statistically significant enhancement in both moisture management and thermal comfort. This advantage is attributed to the presence of tuck loops, which create more efficient pathways for air and moisture transmission. The study establishes that modifying stitch types in knitted fabrics presents a sustainable approach to enhancing sportswear performance without requiring changes in fiber composition or chemical processing.