100% silk buttonhole twist is imported from Japan. It is a soft, three-ply, silk filament thread that is perfect for making hand-made buttonholes and other fine tailoring techniques. In addition to tailoring, this luxurious silk thread can be used for many other fine needle arts. (Britex Fabrics)

Top stitching may require heavier thread to make it stand out. Buttonhole twist usually works well in matching or contrasting colors. Use cotton thread in the bobbin and increase the stitch length for top stitching. (The St. Augustine Record)

Buttonhole twist is a strong, lustrous silk about three times the diameter of normal sewing silk, and is used for hand-worked buttonholes, for sewing on buttons, and for various decorative effects. (Britannica)