Check the manufacturer's tag for the material information. Not all satin is the same. Your satin pillowcases will be made of either silk, polyester, nylon, acetate or any combination of these materials. If you no longer have access to the manufacturer's information, assume your pillowcases are the most delicate of these materials, acetate.
Fill a tub, sink or container with cold water. Add one half capful of delicate fabric detergent as the container fills. If your satin pillowcase contains only nylon, you may add the pillowcase to the coldest temperature wash on your washing machine if you like. Put no other type of satin in the washing machine.
Soak pillowcases under the cold water. Allow to sit for three to five minutes.
Treat any stains that remain. If the satin pillowcase contains stains that do not lift after your initial soak, pour a small amount of the gentle laundry detergent on a rag. Pat the stain with the rag for a few minutes. Allow the pillowcase to sit for a few hours.
Drain the tub, sink or container. Rinse the pillowcase with cold water. Do not ring the material as you rinse it.
Set the towel on a clean, flat surface. Lay the pillowcase flat on the towel and allow it to dry overnight. Do not ring the excess moisture out of the material.