Threads Threads are thin strands of fibers that are used mainly for sewing fabrics together.In the garment industry, threads are super important because: They stitch different pieces of fabric to make clothes. They come in many types — cotton thread, polyester thread, nylon thread, and even special elastic thread. Threads can be strong, stretchy, thick, or fine, depending on the type of garment (like heavy denim jeans vs. a light silk dress).