Natural Gut: Still the gold standard, natural gut-which is made of cow intestine-pockets the ball more deeply across a smaller area, for control, but also allows more of the ball's energy to be returned to the ball, for pop. And you won't find a more comfortable string, so if you have arm problems, natural gut is, well, the natural choice. Gut is the most expensive, it isn't durable (players who hit a heavy ball have been known to break a string in a couple hours), and though companies now use protective coatings, the string is still the most susceptible to losing tension when it's exposed to moisture. Babolat, which produces 90 percent of the natural gut on the market, has many types of gut; we like the Babolat VS Touch.