Fold each piece in half so it measures 20 1/2" x 13". Press the fold line well with a hot iron.
(I LOVE my vintage iron, by the way! Isn't she a beauty?)
Sew near the fold line using an 1/8" seam allowance.
Place the pillow top right side up. Place the backing pieces on top of it, as shown in the photo above. The raw edges of the backing should line up with the raw edges of the pillow top. Folds should be in the middle.
Flip the pieces down into place. There should be an overlap of about 5"-6". (See pin placement.) Pin the layers together around the perimeter of the piece.
Use a walking foot to sew around the ENTIRE piece. I use a 1/4" seam allowance. (You can use a 1/2" seam allowance if you prefer, just be sure to adjust your measurements accordingly.) Reinforce the stitching several times where the backing pieces overlap. These will be the stress points when you are stuffing your pillow form into the cover. The reinforced stitching helps a lot. Trim the corners. Turn right side out. Poke out the corners with a blunt tip scissors.
I love the way this looks....so crisp, clean and tidy! The double layer of quilting cotton is a nice weight for the pillow backing. I've been using this technique for years and they have stood the test of time. If you want to see the pillow front completed, I shared it in this post.
I hope you find this tutorial useful! If you have questions, I'll try to answer them in the comments.
Go forth and make pillows!
(Lots and lots!) :)