bias tape
A narrow strip of fabric, cut on the bias (diagonally across the weave, for greater stretchiness), used in making piping, binding seams, finishing raw edges, etc.
bias tape: diagonal-cut fabric strip for flexible edge binding
Bias tape is a narrow strip of fabric, typically 0.5 to 2 inches wide, cut at a 45-degree angle to the grain of the weave. This diagonal orientation makes the tape stretch and flex with far greater give than a strip cut parallel to the weave. The stretching property is what makes bias tape invaluable: it conforms smoothly around curves, corners, and irregular edges without puckering or bunching.
The tape is used primarily to finish raw edges, bind seams, and create piping on garments, upholstery, curtains, and other sewn goods. When applied to an edge, it wraps around and stitches down on both sides, enclosing the raw fibers and creating a professional, durable finish. On curves especially, the stretch inherent in the bias cut allows even tension as the tape follows the contour without distorting the underlying fabric.
Bias tape comes in single-fold and double-fold varieties. Single-fold tape is folded once lengthwise, while double-fold tape is folded twice, with raw edges tucked inside, making it ready to apply directly without additional folding. Pre-made bias tape in cotton, polyester, and blend fabrics is manufactured in hundreds of colors and patterns. Custom bias tape can be made from decorator fabrics by cutting strips on the bias and folding them.
Bias tape can slip or shift during stitching if not held taut and smooth. Stretching the tape too much during application causes waviness; too little tension leaves slack. On very tight curves or corners under 90 degrees, the tape must be eased and manipulated carefully to avoid puckers. Pressing (ironing) before and after stitching is essential to set the fold lines and ensure the finished binding lies flat.
The term bias comes from the diagonal orientation itself. In textile terminology, the bias is any diagonal line across woven fabric; the 45-degree angle represents true bias, where the stretch is greatest. This property has made bias tape the standard for edge finishing in garment construction, upholstery, and binding since at least the early 20th century.