Flashes: on the bias or no?

[Pleater]

Another difference is that material cut on the bias will stretch more than the same length cut on the warp or weft of the fabric.

This might make them more comfortable when worn, though the stitching might be a problem as it might snap under the tension. Using a zigzag stitch on a sewing machine might give enough stretch, or there are some machines which do straight stitches with built in elasticity for things such as knitted fabric.

Anne the Pleater

[ChattanCat]

Another difference is that material cut on the bias will stretch more than the same length cut on the warp or weft of the fabric.

This might make them more comfortable when worn, though the stitching might be a problem as it might snap under the tension. Using a zigzag stitch on a sewing machine might give enough stretch, or there are some machines which do straight stitches with built in elasticity for things such as knitted fabric.

Anne the Pleater

If your using steam a seam to hold the flashes together, it is pretty stable for sewing.

[The Wizard of BC]

If you look in my tutorial you will see that I eliminate stretch with the fusible non-roll Waistband interfacing.

Once that stuff is stuck on it will not stretch any more.