What is Supima®? Only the best cotton grown in America! With extra long fibers that feel smoother, take dye better and last longer than lesser cottons. It’s rare, too — less than 3% of American cotton is fine enough to wear the Supima name. So you know it makes an exceptional tee.Supima is conscientiously sourced, American-grown cotton that’s farmed to minimize environmental impact. The fibers are 50% longer than standard cotton, so yarns are stronger, softer, less prone to fraying or pilling, and hold color longer.