Window seats are the best place in the house to sit and enjoy a book and a hot beverage, but they aren’t nearly as inviting if they are missing the all-important window seat cushion. Window seat cushions are essentially a flat square or rectangular cushion that covers the surface of your window seat. You don’t need to be a sewing genius to make one, and a DIY window seat cushion will cost far less than a store-bought one.
Measure the top of your window seat to get the cushion dimensions. Cut the foam to these dimensions with the electric knife, wearing the dust mask and goggles to avoid inhaling any particles or getting anything in your eyes.
Lay out your fabric, and cut one piece that is 1/2 inch wider on all sides than the size of the foam, for seam allowance. Cut two pieces: one that is one-fourth the size plus 6 inches of the first piece of fabric, and one that is three-quarters the size plus 6 inches of the first piece of fabric. This will be the back of the pillow, and the extra 6 inches will overlap to form the slot for inserting the foam.
Cut two strips of fabric as long as the foam is wide, and 4 inches wide. Cut another two strips, as long as the foam’s length, and 4 inches wide. These are the side panels of the cover, with seam allowance.
Pin one short strip to a long strip, then the second short strip followed by the last long strip, and sew together on the wrong-side of the fabric, so that you have one very long strip. Pin the strip around the outside of the first piece of fabric cut, matching the short sides and long sides, on the wrong side of the fabric. Sew together.
Fold a single hem under the edge of both the quarter and three-quarter fabric pieces, then sew the hem. Pin the two pieces to the edge of the side strips already sewn onto the cushion cover top, wrong-side out. Make sure the quarter piece overlaps the three-quarter piece by 6 inches. Sew the two pieces on, leaving the overlap open.
Invert the cushion cover, so it is right-side out, and poke the corners out, so that they are square. Insert the foam piece through the overlapping gap at the back, then position your window seat cushion on top of your window seat.