This paper presents models of yarn cross-sectional shape in plain woven fabric. Various yarn and fabric parameters, including fiber type, yarn count, yarn twist factor, and cover factor, were used as control factors to produce fabrics with known properties. New algorithms were successfully developed from the real fabric images to create realistic yarn models. The fabric images were obtained through the synchrotron technique which provides high-quality yarn and fabric cross-sectional views without disturbing the yarn and fabric structure. The changes in the shape of yarn cross-section along the yarn were examined. The yarn cross-section was modeled by elliptical and polynomial curves. The approach can be expanded for 3D modeling of woven fabrics.