Mock Box Cushion

foam
fabric
measuring tape
zipper

Steps:

1. The seams on a mock box cushion are located halfway around the sides and the corners are simply clipped to square off the cover. Start by measuring the length of the foam across the top plus half way down each side and add one inch for seam allowances.
2. Repeat in the opposite direction on the top of the foam, measuring from front to the back and halfway down the sides and add 1-1/2 inch for seam allowances.
3. Cut two pieces of fabric to the same size for the top and bottom of the cushion. With right sides together, pin the back edge of the cushion sections together, and then mark where the zipper will be located. Use a one-inch seam allowance to stitch the pieces together, basting at the location of the zipper.
4. Install the zipper following the manufacturer’s directions for a centered zipper installation. With it open, place the right zipper tape face down on the seam allowance with the coil next to the seam and pin. Starting at the bottom of the zipper, machine-baste the right zipper tape in place through the zipper tape and seam allowance only. Close the zipper and keep the pull tab up. Extend the left seam allowance; pin and machine baste the zipper tape in place. Topstitch on the outside of the cushion and remove the machine basting.
5. With right sides facing, pin and sew the remaining sides and front edge together using a half-inch seam allowance, and then press the seams open.
6. To create a mitered corner, separate the layers of fabric and fold them in such a way as to line up a side seam with the front seam. Center the seams and pin in place. Measure the depth of the foam and draw a line the same measurement as the foam, perpendicular to the seam. Stitch along the line and trim the fabric close to the stitching. Repeat this for all four corners.
7. Turn the slipcover right side out; insert the foam and close the zipper.