Sirospun spinning system enables two-folded yarn production in a single step process and this system can be installed on conventional ring spinning system with low investment costs. Sirospun yarns have higher tenacity, lower hairiness and better evenness values compared to conventional ring spun yarns. Besides, system offers advantages such as eliminating doubling and twisting processes. System provides increase in the production, production costs, savings on place and staff due to eliminating some processes. In this research, properties of 100% PES ring spun and sirospun yarns were compared and the influences of spindle speed and twist coefficient on the properties of 100% PES sirospun yarns were investigated.