When possible, I prefer to sleep under or on top of silk. The tightly woven, natural fibers in silk sheets and pillowcases are hypoallergenic compared with cotton or synthetic fibers. This makes silk a great option for sensitive skin like mine. Silk also prevents moisture loss from the skin while sleeping.
In the morning, your face will be better hydrated after sleeping on a silk pillowcase. In addition, there are benefits for your hair. Sleeping on a cotton pillowcase will cause hair to bunch, knot, and develop static electric charges. On a soft silk pillowcase, however, hair will slide, which is much less damaging. Limiting bed-head is essential when you get as much beauty sleep as I do.