Iron Bias Strip Before Sewing To Curved Edge
One of the trickiest aspects of sewing a bias faced curved neckline is aligning the bias facing strip to the curved neckline edge. Even if the bias cut fabric strip has a good amount of stretch and flexibility, molding a straight edge to curved edge feels a bit unnatural and uncomfortable.
A simple trick you can use to make the alignment and overall construction process easier and more comfortable, is to pre-iron the bias facing in a curved position to imitate the neckline curve. This should be dine after the bias fabric strip is folded and ironed down the center. Ironing a bias strip in a desired curved position is called shaping and is often used when clean finishing curved edges (neckline and armholes) using bias facings, binding, and any other bias-cut strip used to clean finish these edges,
If you utilize the pre-ironing trick shown above, you'll see a big difference in how much easier it feels to align the bias facing to the curved neck edge. The bias strip lays flatter and molds much easier to the curved edge it finishes.
This difference can also be felt when the bias facing is complete and flipped to the inside of the garment. In this final position, the bias strip lay flush against the wrong side of the garment surface which encourages a smoother finished edge and a tension-free application.