The best threads that you can use for sewing leggings are textured threads, such as polyester and nylon threads. Examples of such textured threads are the Best Stretch and the A&E's Wildcat Plus. Textured threads are highly recommended for sewing leggings since they offer perfect seam elasticity and coverage. This makes them ideal for the cover stitch and over-edge seams present in leggings. These seams are responsible for the high strength, stretch, and comfort offered by leggings.