A sheen elastic with a definite rib texture . Heavier weight, used for sports items, so not as stretchy as the thinner matt fold-over.  Often this foe will be used around the garment and continue on to the strap.  (where used for straps, its advisable to use a reinforcement tape inside to remove the stretch to prevent the stitches popping).

Used on the Maris sports bralette and referred to as grosgrain fold-over.  We have a strap version to match, search 3D ribbed

16mm is the flat width.