Cotton is made of natural cellulose fibers that are soft, breathable, and slightly flexible.
When you move, sit, or pull on the fabric, those fibers elongate — especially in areas under tension, like the shoulders, chest, or sleeves.
Unlike synthetic materials, cotton doesn’t have built-in elasticity (no spandex or lycra), but its natural structure allows for gentle give that increases comfort with wear.
That’s why a new 100 percent cotton t-shirt might feel a little firm at first and then gradually mold to your body shape — in the best possible way.