It's the Look and Feel
For most people, satin sheets are great for two reasons:
- Smoothness comes from the small size and tight weaving of the fibers. The tighter the weave, the smoother the surface - often described using a term called "thread-count." In order to pack so many threads in a small space, the threads must be very thin. Imagine how rough a sheet made of button thread would be! Man-made fibers like polyester, nylon, and acetate can be made very fine, which makes them perfect for high-thread-count fabrics.
- Shininess comes from the type of thread. Very few natural fibers are shiny; so usually you must use a man-made fiber like polyester, nylon, or acetate to get a shiny surface. In fact, you've probably seen sheets described as "Sateen." These are usually cotton sheets with very high thread counts (over 300 per inch) that feel as smooth as normal satin sheets, but since they are made of cotton, they are not shiny. So they really aren't satin as the world typically views it.