Pillow shams are a decorative pillow case that typically features flanges as a decorative effect. In order to make the flanges appear symmetrical with the rest of the case, you must miter the corners when sewing it together. Mitering is the process of positioning two objects, in this case flanges, at a 45-degree angle to each other and forming a 90-degree angle at the top. When you combine four mitered edges, you have a rectangular shape.
Cut the fabric. You should have one rectangle measuring 20-by-29 inches and two smaller rectangles that are 20-by-15-1/2 inches. This is the main part of the pillow sham. Cut two more rectangles measuring 26-by-5 inches. Cut two more rectangles measuring 35 by 5 inches. The last four rectangles are the flanges.
Position the three main pillow pieces with the wrong sides facing out. The hemmed edges should be in the center of the back side of the sham.
Fold the flanges in half with the wrong sides out. Cut the edges to a 45-degree angle and pin the flanges together with the right sides pinned together. This should form a rectangular tube.
Sew the angled edges together. Fold the seams out and press so the fabric is as flat as possible.
Fold the flange with the right side of the fabric out and press again for sharp edges around the outside.
Pin the right-sided flange. The edges against the outside edges should match those of the wrong-sided sham. The flange should be sandwiched between the two layers of fabric.
Sew along the entire sham 1/2 inch from the edge.
Turn the sham right side out and press the sham and flanges.