How to sew a neat envelope cushion back
Measure 2 fabric panels for back, as wide as cushion front. For the length, measure 2/3 of cushion front length and add 4cm. Cut out.
Press 2cm of 1 long edge on each panel to wrong side, then fold over another 2cm and press. Topstitch 1cm in from edge.
Lay cushion front right side up. Put backing pieces right side down on top of cushion front, aligning raw edges with front and overlapping hemmed edges. Pin pieces in position.
Using a 1cm seam allowance, stitch around all sides (see diagram, right).
Trim corners. Turn through and fill cover with cushion insert through back opening.