This study examines the appearance characteristics of collars produced through fused deposition modeling (FDM) 3D printing by analyzing the interaction between collar types and infill structures. Three collar types-stand, convertible, and shirt-and three infill structures-rectilinear, gyroid, and honeycomb-were selected to generate nine collar samples. All samples were modeled in CLO 2025 with identical base dimensions and printed under consistent FDM settings using TPU filament to ensure comparable structural conditions. Appearance evaluations were conducted by 12 experts in garment construction and fashion design through an online survey on the naturalness and visual quality of each collar using a 5-point Likert scale. The findings revealed that the optimal infill structure varied depending on collar type. The stand collar exhibited stable appearance evaluations across all infill structures, with the gyroid structure receiving the highest evaluations. The convertible collar showed the greatest sensitivity to infill structure, with the rectilinear infill structure producing the highest ratings for both naturalness and visual quality. The shirt collar demonstrated the lowest scores overall due to its structural complexity; however, the honeycomb structure was relatively more suitable. ANOVA results confirmed statistically significant differences among collar types for the rectilinear and gyroid structures, but not the honeycomb structure. This study provides empirical evidence that internal geometry plays a critical role in determining the silhouette quality of 3D-printed garment components. The results offer practical guidelines for selecting infill structures tailored to specific collar shapes and contribute foundational insights toward the development of modular, seamless garment systems.