I don't know why I didn't review these before when I've been using them for over ten years now. IMO/E silk/satin pillowcases can protect the skin and hair from wrinkles and split ends. The idea behind this is that satin is slippery and helps prevent wrinkles and creases in the skin from repeatedly sleeping in the same position and having the facial skin rubbing against cotton.
As for the hair, it helps with retaining moisture in the hair as well as preventing split ends - the idea being that cotton is rougher and the ends of the hair get dried out and are more prone to breakage. All I know is that when I slept with cotton cases on my pillow I sometimes woke up with creases on my face. I have not experienced this with silk/satin pillowcases.
I buy mine from Dharma Trading. If you wash them carefully in mild detergent in a lingerie bag on the gentle or hand-wash cycle and let them air dry they will last a long time. DT's are properly made with finished seams and hems.
NOTE: I have also purchased silk satin fabric to make my own cases and head wraps with the same results.