Supima is the best cotton grown in the country. With extra-long fibers that feel smoother, take dye better and last longer than lesser cotton. It s rare, too — less than 3% of American cotton is fine enough to wear the Supima name to assure you it makes an exceptional top.Supima is conscientiously sourced, American-grown cotton 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..