Use fine machine embroidery thread for chiffons, silks, and other lightweight, delicate fabrics. Don't be tempted to try general purpose thread on fine fabrics because the thicker thread will make the fabric pucker where seamed. Buttonhole twist thread is not used for buttonholes. It is used for topstitching. Always use an N-needle with buttonhole twist thread.
Regular needles cause fraying and create odd-looking stitches.
Decorative metallic thread should always be used with an HE or embroidery needle. Any other type of needle can cause the thread to shred. Rayon thread is too weak for joining a garment but is wonderful for topstitching and making buttonholes. It comes in regular and fine weight and makes seams that are almost invisible. One-hundred percent cotton thread is perfect when stitching silk because it won 't stretch.