For years, Babolat VS Gut has been considered the gold standard when it comes to natural gut and strings in general. Even popular multifilament strings like Tecnifibre X-One Biphase and Wilson NXT compare their properties against natural gut, with Babolat VS being by far the most popular.
When I first used VS, it came uncoated, and a separate bottle of coating was purchased and periodically applied. Recently, this coating was applied at the factory before packaging and sold as VS Gut with Thermogut technology. This was basically a fancy way of saying that it had a coating applied that helped to protect from fraying and the elements like humidity and heat a small amount. The newest iteration of Babolat’s natural gut uses a more advanced coating, which they refer to as BT7, promises 15% more longevity, 25% greater durability, and 60% better resistance to humidity. That is a lot of benefit to gain from merely changing the coating of the string.
The new BT7 coating is only part of the story though, and the other part gets hidden behind the promise of longer lasting natural gut playability. In order to increase the durability as promised, Babolat has chosen to go with larger individual fibers, and use fewer of these larger fibers. These thicker fibers are also bonded in a special layering procedure that aligns the fibers in a more efficient way, decreasing the amount of resin necessary. While these changes do increase the durability of the string, they come at a cost.
This cost is really in the perception of the player. The combination of thicker fibers, different alignment, and reduction in the amount of binding resin used all result in a string that feels stiffer than the previous Thermogut version. While many probably do not remember the original, uncoated VS, the thermoguard coated iteration has been available for awhile and garnered its own following. The new BT7 VS Gut will play stiffer, but it is up to the player to decide if that is a positive or negative feature. What may be a comparison of soft vs. stiff to one, could be a comparison of mushy vs. crisp to another.