Envelope-style pillowcases are made by using just one long piece of fabric or three pieces of fabric. Different kinds of shams can be added in the design to improvise and add to the decor.
A very simple pattern of an envelope-style pillowcase is to overlap a long piece of fabric at the back and stitch it at the sides. Another pattern is to join three pieces of fabric together, a big piece for the front and two smaller pieces for the back. Pillow shams spruce up the room, so depending on one's creativity and tailoring expertise, an extra seam at the sides or buttons, tassels and trims can be added.