As interest in personalized biomechanical interventions grows, customized insoles have garnered attention for their ability to improve plantar pressure distribution and foot comfort. While previous studies primarily focused on pressure redistribution, systematic quantitative evaluations across different foot types remain limited. Notably, objective assessment methods that link plantar pressure-based structural metrics with subjective comfort are still insufficient. In this study, customized insoles were fabricated for 32 adults using plantar pressure-based foot shape acquisition and additive manufacturing, and their biomechanical effects were evaluated. The arch index (AI) and subjective comfort were measured before and after one month of use. AI was calculated from static plantar pressure data, and comfort was assessed across multiple foot regions using a visual analogue scale. Statistical analysis revealed significant improvements in comfort at the arch, ankle, and rearfoot regions (p < 0.05). The mean AI deviation from the normal reference value decreased by approximately 30.6%, indicating a shift toward a more normalized arch pattern. Overall, this study demonstrates that customized insoles can enhance plantar contact characteristics and perceived comfort across different foot types. These findings provide quantitative evidence for engineering evaluation and establish a foundation for the objective assessment of personalized insole performance.