Use a lighter to burn the edge of the silk material. The real silk does not see an open flame, and has the smell of burning hair. The ashes become black granular, which can be crushed by hand. Simulated silk, such as rayon (viscose), has a paper-burning smell when burned, showing a little off-white ash; burning polyester will cause flames and black smoke, and after the fire is extinguished, it will appear as hard and black beads.