Waxing thread and cord makes it stiffer, more water and mildew resistant, and stronger. It is mainly used in hand sewing that requires strong, long lasting, water-tight seams. It is also great for machine sewing for those willing to clean the thread's waxy residue. Waxing thread and cord makes it stiffer, more water and mildew resistant, and stronger. It is mainly used in hand sewing that requires strong, long lasting, water-tight seams. It is also great for machine sewing for those willing to clean the thread's waxy residue.