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In upholstered furniture, the piping cord is usually made of paper. If you plan to wash your slipcover, you must purchase cotton piping cord. Paper cord will be stiffer, but the main reason it is used in manufacturing is cost, as the cotton cord is a little more expensive. Purchase a good quality cord, the diameter should be solid and consistent, as the quality of the cord will greatly affect the finished product. The standard cord size used in furniture manufacturing is 5/32", or 0.4 cm. This cord will be commonly referred to as piping cord in the garment trade, but in the furniture trade, welting or welting cord is the common name. Both terms refer to the same product.
As shown in the photos, there are two ways to assemble piping fabric, as you will rarely be able to cut one continuous length of piping.
Once the lengths of piping have been assembled, fold the fabric over the piping cord and sew with a piping foot or zipper foot.
If you are sewing a very thin fabric, you may find that a standard piping foot will not sew a tight piping cord. When the purchase of a smaller piping foot does not suffice, you may have to use Teflon tape to fill the piping channel. In commercial production, feet are machined to precise measurements.
Continuous zipper is sold on rolls and the zipper pulls are often purchased separately. The tape of continuous zipper is printed with arrows. Start the zipper pull at the end of the tape which shows the top of the arrow.