Bias binding tape or polyester bias binding tape is a narrow strip of fabric, typically plain weave, cut on the bias. As the weave of fabric is at a 45 degree angle, the resulting fabric strip is stretchier than a strip cut on the grain. The strip also has a better drape, and conforms to curves better than fabric cut on the grain.
Bias binding tape is used in making piping, binding seams, finishing raw edges, and is also used decoratively. It is often used on the edges of quilts, placemats, and bibs, around armhole and neckline edges instead of a facing, and as a simple strap or tie for casual bags or clothing.