Measuring and Cutting the Materials
Round the front edge of the foam. Using a compass, draw a half circle at the leading widthwise edge of the foam, on both sides. Make sure you put the marks on the front of the foam, leaving the back edge square.
Trim the foam to the shape you have drawn, by shaving the foam away to create the curve or "bullnose" at the front of the cushion. Use a pair of scissors, a knife, or an electric carving knife.
Starting at the back of the foam, measure all the way around the lengthwise -- front to back -- edge of the foam, including the height, top and bottom. Measure the foam from side to side. Note both of these measurements.
Lay the fabric out on a flat surface.
Using the first measurement -- the foam's length all the way around -- mark the correct measurement lengthwise on the fabric. At the top and bottom of this first measurement, mark the width -- second measurement -- of the foam. Connect these lines, creating a large rectangle. Cut out fabric leaving 1/2 inch seam allowance all the way around.
Turn the foam up on its side and place it on the fabric. Trace around the edge of the foam, making sure to include the rounded edge. This will be your side piece and it should be U shaped. Cut 2 identical pieces, leaving 1/2 inch seam allowance all the way around.
Assembling the Cushion
Pin and stitch the long piece of fabric to the side piece of fabric, using 1/2 inch seam allowance. Clip the curve around the front of the cushion cover for the bullnose shape. Fold the seam allowance at the edges of the lengthwise piece over at the back to use for zipper placement. Repeat for the other side. When you are finished, you should have a big bag with U-shaped sides.
Insert the zipper. The zipper measurement should be 1/2 inch longer than your width measurement for your cushion. Pin the zipper to one side of the opening left in the back of the cushion cover. Stitch down with zipper foot. Leaving the zipper closed, pin the other side of the zipper to the remaining side of the opening. Unzip the zipper and stitch down.
Insert the foam into the cushion cover. Zip closed.
Things You Will Need
- Knife suitable for cutting foam, or electric carving knife
- Sewing machine
- Custom length zippers can be purchased at most fabric stores and upholstery stores. Zippers that are too long can be shortened by inserting a zipper stop in the appropriate place at the bottom of the zipper, then trimming the end of the zipper and burning the cut edges so they don't fray.