- Measure the area in which the cushion will sit. Purchase a piece of foam rubber and cut it to the measured size. Many times there are precut cushion sizes available at fabric or upholstery stores. Measure the thickness of the foam and all the way around the outside.
- Create a pattern for the size of the cushion and another pattern for the strip of fabric that wraps around the side of the cushion (both length and width). Add a 5/8-inch seam allowance on all sides. Draw the pattern on cardstock, poster board or graph paper. You may have to tape smaller pieces of paper together for it to be large enough for your cushion size. Cut out the pattern.
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Purchase a water resistant, durable fabric for your cushion. Cut out the fabric from your pattern. Sew a zipper in the long side piece so it will fit at one of the sides. This will be the back of your cushion when it's finished. Pin and sew the short ends of the long, side strip with the right sides together. Press the seam outwards.
Pin one of the two cushion pieces to the strip with the right sides together. Sew a 5/8-inch seam, easing the corners by clipping the fabric on the seam side as you go. Repeat the same procedure with the other piece of fabric onto the opposite of the fabric strip. If you are not attaching a zipper, leave a 5-inch opening. - Turn the cushion cover right sides out by unzipping the zipper. If no zipper was attached, turn the cover through the opening. Stuff the foam piece into the cushion cover. For the non-zipper style, fold the fabric inward at the opening to match the seam allowance. Hand sew the opening shut by hand.
