The simple knife-edge cushion involves sewing together a top and bottom fabric and stuffing it with foam or batting for loft and providing a way to fasten it to the chair to prevent it from slipping off. Ribbon or self-fabric ties will allow you to tie it to the chair posts. Velcro attached to tabs can also anchor the cushion to the chair. Trace a pattern or template of your chair bottom on paper. This allows you to customize your cushion to the shape of your seat. If the chair is asymetrical from back to front, mark your pattern accordingly. Also mark where you want the ties to be for securing the pillow to the chair. They need to be directly in front of a spindle or post, at the chair's back, one on each side of the cushion. Add seam allowances. Use the pattern to cut your fabric. For stuffing, 1 to 1 1/2 inch foam or Polyfil batting will suffice.
Box or Gusset Cushion
The box cushion design includes a side piece, known as the gusset, that adds depth or girth. The gusset piece can be one length of fabric as wide as the foam pad plus seam allowances. Figure the gusset length by adding two widths and two lengths of the pillow top. Sew the top and bottom pieces to the gusset. Mark the cushion where you want the ties to attach to the chair posts or spindles. Sew the ties or tabs at the marked positions along the bottom seam line. Wrap high-density foam with batting and fill the cover. Add 2 to 3 inches of foam for cushy comfort.
Rounded Edge Cushion
To obtain girth without a separate gusset piece, use a method that falls in between the box and knife-edge cushion--the rounded edge. This style involves two pieces of fabric, a top and bottom, that are sewn together. Where the corners of the material meet, the fabric is pinched together at right angles and sewn for a few inches forming a triangle of stitches at the corners, much like a tote bag whose seam forms a flat bottom. This gusset without a separate strip of fabric allows for more stuffing than a knife edge pillow. It also needs ties or tabs sewn into the back seam for keeping the cushion in place.
Tufted Cushion Variation
Any of the cushion styles mentioned above can be tufted. Tufting means that buttons or stitches are sewn from back to front after the stuffing is inserted, creating puffy segments in the pillow which add a classic design detail. Strong upholstery weight thread and a long, large-eye needle or a curved needle work well for attaching buttons. You can omit the buttons and just make stitches where buttons would be, pulling the thread taut to cinch the padding enough to make indentations that create the puffiness. A center button only or a grid pattern of buttons or stitching vary the look of the pillows. They, too, use tabs or ties at the back to attach the pillow to the chair. To protect the wood from being scratched by the buttons, add 3 inches or more of padding to the cushion. However, if scratches on the wood are a particular concern, use the buttonless method.
Piping is another variation for adding style to a cushion. You will need enough piping to span the width and length twice for each seam, plus another inch. For box cushions, sew 1/8- to 3/8-inch diameter piping covered with a contrasting fabric into the seam line at both top and bottom seams; for knife-edge cushions. For another style variation, cut 1 1/2-inch wide ties long enough to tie bows at the chair posts for a feminine look, or add a short skirt to the cushion to hang about 5 inches below the seat of the chair. The skirt is sewn into the lower seam (the part that touches the chair bottom) and should have inverted pleats where the corners of the cushion meet to allow ease in turning the corner.