Can we do a swimwear waistband, that is similar to a retail ready to wear the garment. We can come close.
Will be using only a home sewing machine, the retail version is down with an industrial custom made serger like machines. You can do something similar with a home cover stitch machine. Most do not have one so home sewing machine it is.
I have an old swimsuit, that is poly/spandex, going to be using a cotton/spandex (don’t have any red poly/spandex).
The following is my preferred method for doing swimwear, for both the waistband and leg openings. I most often use rubber elastic it performs better over the life of the garment, the regular elastic will wear out far sooner, and sometimes do not perform as well as rubber in water.
1/2″ or 5/8″ rubber elastic for waistbands and 1/4″ or 3/8″ rubber elastic for leg openings.
Using 100% polyester thread, do not use a cotton or cotton blend thread with swimwear fabric.
First I have sewn in the elastics with a slant stitch, then folded over and topstitched from the front. Use the triple thread/stitch stretch stitch.
Did not use a twin needle to do the topstitching, I prefer single needle stitching,
I used rubber elastic (have to order online), on other and braided elastic (available everywhere) on the other
Results are similar, in looks from the outside, different from the inside, about the same amount of stretch as the swimsuit,
Special note, rubber elastic smells awful, I wash the entire amount when I get it, and will still stink when all in a container for a short while, the smell dissipates after you put in the garment.