The process goes like this: Once cotton has been processed from its raw form into rough yarns of smaller and smaller size until they're suitable for your standard T-shirt thread, the process is largely finished. With ring spinning, there's an extra step: Yarns are rapidly spun around a ring mechanism (hence the term) and onto a large bobbin, which thins the yarns into a finer gauge and, more importantly, twists the fiber into a consistent direction. Those bobbins are then wound into larger spools of cotton for commercial sewing.
"Open-end” cotton that doesn't undergo this process is perfectly usable, but is coarser—look at it under a microscope, and it will appear frayed and jagged. Ringspun cotton, on the other hand, has all of its fibers neatly spun into a smooth twist with a tighter texture. It's a relatively slow and unnecessary process as far as the bottom line is concerned, but produces yarns that are finer, smoother, and softer. Which creates garments with the same properties.
T-shirts and other cotton items made from ringspun cotton tend to be softer and smoother to the touch compared to coarser open-end cotton ones, and are often (but not always) lighter weight due to the tension and fine weaving of the ringspun yarns It also has a reputation for greater durability; with the yarns all twisted taught in a consistent direction, there's less likelihood for the strands to fray or break.
This intersects with the idea of ‘singles’ in cotton, which correlates with the weight, heft and overall feel of a shirt. Most ringspun shirts might sit around 30 to 40 singles, while heavyweight tees hit closer to 18 singles. With the higher single count, the tighter the cotton can woven together due to its finer build and feel; the higher the single count, the slimmer and lighter the shirt will feel.
Combing the cotton adds another layer of quality to the cotton in use. This means combing each fiber to create a more uniform and streamlined material. While this will tighten up stray strands and remove impurities from the overall fiber, the final product will be noticeably smoother to the touch.
While it's not terribly common—or, at least, clothing manufacturers don't often tout its use—ringspun cotton can produce some terrifically soft and high-quality cotton whose benefit is entirely focused on the wearer: Greater comfort, more longevity and a finer hand feel. Even if something is touted as “100 percent cotton,” it’s also worth sorting out how the cotton fibers are constructed and processed; put simply, 100 percent cotton material will always feel more luxe as long as its ringspun, combed and crafted with higher single number. When it is used, it's often in T-shirts, though it's also found in denim as well; "ringspun denim" usually means that the warp threads only have been ringspun, while "ring-ring" means that both the warp and weft use ringspun yarns.