Controls if the back is made of of a single piece of fabric cut on the fold, or as two mirrored pieces that are sewn together down the center.

Advantages: Saves a construction step, removes a seam, may be more comfortable.

Disadvantages: Doesn’t work with zippers, harder to fit a larger pattern piece on the fabric (may cause more fabric waste).

Zippers:

If using a back zipper, do not enable this option.