The more I think about it they are either Spandex or DenimThis is true for many companies as well. They say silk dome. Some seprate it from Silk, or Textile, or polyester, Tetolon, etc. Some group them all togther. But in the end it's not down to the material implemented, its how the design as a whole is executed. There are poorly performing pure silk domes and there are very high end (great sounding, low distortion, etc.) polyester or textile domes.