Bias Binding: Making and Applying It

Bias binding works because of what happens to a woven fabric when you cut it at 45 degrees to the warp and weft. In a strip cut on the straight grain, yarns run the full length and the strip cannot lengthen. In a bias strip, no yarn runs from one end to the other. Research on bias cut woven samples describes this precisely: no yarn is held at both ends, so the structure carries load through friction at the interlacing points, and behaviour depends strongly on sample width. The yarns can rotate and the interlacings can shear, so the strip extends, narrows, and moulds itself around a curve without wrinkling.

Cutting Bias Strips

Find true bias by folding a cut edge of fabric so that the crosswise grain lies parallel to the lengthwise grain. The fold line is the 45 degree bias. Cut strips parallel to that fold using a rotary cutter and a long ruler.

For any quantity, the continuous bias method saves time. Cut a square or rectangle of fabric, slice it corner to corner into two triangles, join the two short straight-grain edges to form a parallelogram, mark parallel strip lines across it, then join the remaining two edges into a tube with the marked lines offset by exactly one strip width. Cutting along the marked line spirals around the tube and yields one continuous strip.

Join separate strips on the straight grain, not the bias. Lay two strips right sides together at right angles, stitch across the diagonal, trim to 6 mm and press open. The diagonal join spreads the bulk of the seam across the width of the binding instead of stacking it in one place, so the finished binding does not develop a lump.

Width and Fold Types

Single fold binding has both long edges pressed towards the centre. Double fold binding is single fold binding folded again down the middle, so it wraps an edge with a finished fold on both faces.

The arithmetic is straightforward. For double fold binding with a finished visible width of W, cut strips four times W plus a small allowance for the turn of the cloth, typically 3 to 6 mm depending on fabric thickness. A finished width of 6 mm therefore needs a strip of about 25 to 28 mm. For single fold binding used as a facing that will be turned entirely to the inside, cut roughly twice the finished width plus two seam allowances. Always test on a scrap of the real fabric, because thick cloth eats more width in the folds than the formula predicts.

Applying It

The two step method gives the cleanest result. Open one fold of the binding, pin its raw edge to the raw edge of the garment right sides together, and stitch along the pressed crease. Then fold the binding over the edge to the wrong side and secure it, either by hand slipstitching, by machine stitching in the ditch from the right side, or by edgestitching close to the folded edge. Slower, and worth it on anything visible.

The one step method encloses the edge in the folded binding and stitches through all layers in a single pass, usually with the help of a binder attachment. It is fast and standard for quilt edges and for utility items, but keeping the underside caught consistently takes practice. Setting the binding slightly wider on the underside gives you margin for error.

Necklines, Armholes and Corners

Around a concave curve such as a neckline or armhole, gently stretch the binding as you pin the outer edge, because that outer edge has to travel a shorter path once it is turned. Do not stretch it around a convex curve, where the opposite is true. Pre-shaping the binding by pressing it into a curve with the iron before pinning makes both cases much easier.

At an outer corner, fold a mitre by stitching to the seam allowance distance from the corner, backstitching, folding the binding straight up, then folding it back down along the next edge. The diagonal fold that forms is the mitre.

Finish a continuous binding by joining the two ends on the diagonal before the final centimetres are stitched down. This produces one uninterrupted binding with no visible start or stop, and it distributes the join bulk the same way that the diagonal strip joins do. Because binding sits at an edge that will be handled and washed repeatedly, stitch quality matters, and stitch length and needle choice measurably affect how a stitched edge withstands load and deformation.