If incredible softness is a top priority when you’re shopping for clothing, you most likely own a lot of modal. Technically a type of rayon (a.k.a. viscose), modal fabric is known for its silky feel.

For well over a century, viscose rayon has been used to make clothes, tires, cellophane and everyday kitchen sponges. It was hailed as a wondrous new product when first introduced — but what most ...