Piped seams on chairs serve more than just a decorative purpose. The welting protects the seams exposed to constant wear. Instead of the seam taking the hit, the piping stands up from the seam and takes the brunt of the wear. While you can buy piping in specific colors from a fabric store, it doesn't take much to make your own. That way, the chair's piping can be in the same fabric as the upholstery. You can use bias tape or fabric in a contrasting color if you want to add pizzazz to your project.
Measure the length of the seams where you want to add piping. Most upholstery piping is used on the arms and back of the chair, on the seat cushions or sometimes on the lower portion of the chair to prevent wear by the legs.
Cut the cording to the length measured for the fabric seam, plus a few extra inches. Set the cording aside temporarily.
Lay out a piece of fabric on the cardboard cutting board in the same way as it came off the fabric bolt, in a single layer. Since upholstery fabric is generally larger than the standard 45 inches wide, most chair piping won't be longer than that, unless it has a wide back. If you need additional fabric to make your piping, you can sew two strips of fabric together to make it longer. Because each strip is only an inch or so wide, you'll need roughly 1 yard of fabric to create 21 yards of piping.
Cut a single strip of fabric on the diagonal or cross-grain of the fabric. The strip will be twice as wide as the cord, added to twice the measurement of the seam allowance. For example, if you have a 1/8-inch cord, multiple that by 2 to equal 1/4 inch. If you want a seam allowance of 3/8 inch, multiply that by 2, which equals 3/4 inch. Add the two measurements together to get the strip's total width of 1 inch.
Fold the fabric strip over the cord, matching the long edges, and pin it together.
Insert the zipper foot onto your sewing machine, following the instructions in the manual for your sewing machine. Generally this calls for loosening a small round knob near the back of the unit where the foot attaches to the rod. Tighten it thoroughly once you slip the foot over the rod.
Set the zipper foot to the right of the cord. Sew along the entire length of the cord as close to the cord as possible, removing the pins as you sew. Finish the ends by reversing the stitch to lock the threads in place. Cut the extra threads.
Insert the piping between two pieces of upholstery fabric, with its edge matched to the edges where you will make the seam. Pin the fabric with right sides together at the seams. The cord should be on the inside of the two layers.
Sew the layers of fabric together, again using the zipper foot. This allows you to sew the seam as close to the edge of the cord as possible. Remove the pins as you sew. After sewing, turn the fabric layers right side out to view your work. If you have sewn it correctly, the piping should be tightly sandwiched between the seams, not sewn over.