Madeira Aerolock Thread is a strong, premium, 100% polyester serger thread. It holds color even after years of laundering. It's composed of 2-ply, core-spun thread and is suitable for use in your overlocker's needles and loopers. Like all Madeira thread, each cone undergoes extensive quality testing to ensure you have the best serging experience. Each spool stands approximatley 6" tall.