This study was to investigate the effect of processing variables in the foam sizing of new synthetic filament yarn such as size add-on, size content and drying temperature to improve weaving performance. The new synthetic filament yarn was required to be size at a low temperature. The flaming characteristics of copolyester resin, the influence of viscosity in the size solution, the framable concentration, the abrasion resistence photographs of cross-section of sized yarn were demonstrated. The product such as water dispersible copolyester of relatively low viscosity had a high degree of penetration in the yarn. The strength and elongation of sized yarn were not proportional to the size add-on. The size add-on level was required .to achieve the level of abrasion resistance necessary to weave the yarn. As a result, the properties of new synthetic filament yarn sized using foam were equivalent or superior to those of similar yarn sized conventionally.