This study presents a technical analysis of men’s T-shirt development within a CLO3D virtual environment, focusing on the integration of digital pattern development, fabric simulation, avatar customization, and virtual fit evaluation into a unified apparel development workflow. Unlike previous studies that primarily discuss the general advantages of 3D virtual prototyping, this research provides a garment-specific technical investigation of men’s T-shirt simulation and evaluates the practical effectiveness of CLO3D in improving workflow efficiency, fit accuracy, and sustainable product development. A simulation-based experimental methodology was adopted, incorporating digital pattern construction, sewing simulation, fabric parameter assignment, strain and stress mapping, and real-time visualization. The results demonstrate that CLO3D enables structurally accurate garment development with realistic drape behavior and effective fit assessment through iterative virtual simulation. The study further confirms that digital prototyping significantly reduces physical sampling requirements, material dependency, and development time while improving design communication and workflow flexibility. However, simulation accuracy remains highly dependent on correct fabric parameter calibration and user expertise. The findings contribute to a clearer technical understanding of CLO3D-based apparel development and support the broader adoption of digital garment engineering in sustainable apparel production.