This model could be used for swimsuits or underwears depending of the type of fabric. I have made the pattern out of my favourite bikini pants. The seam is a decorative stitch on my sewing machine that could be stretched without breaking. The thread used is Wooly Nylon.
When sewing in fabrics with an extra stretch (like swimwears etc) I like to use this special thread, Wooly nylon. With this in the upper and lower loopers of the Serger machine you get really stretchy seams.