Sometimes a sweater pulling in at the hem is a good thing, sometimes a bad thing – it all depends on your individual shape. But by using a single crochet ribbing in a yarn without too much elasticity, you get the strong vertical lines without uncomfortable tightness at the waist.

Silks, cottons, linens, bamboos and blends of all of those are not very stretchy fibers. Elasticity is something to take into consideration when selecting a yarn for any project; sometimes you want it and sometimes you don’t.