Called shirring. Even so, the glance it results in is similar to smocking, and that is an embroidery technique that’s been around an extended while. But maybe don’t google “what's smocking” cuz apparently Additionally, it refers to a thing that has very little to try and do with sewing… Anyway, https://coveredspandexyarn40493.boyblogguide.com/30932913/what-does-double-covered-yarn-mean