Babolat Xcel 16 660' The Babolat Xcel 16 tennis strings give players excellent comfort and durability on the court. The soft polyamide structure and multifilament composition provide exceptional elasticity. Perfect for players with arm issues, these strings provide a soft, comfortable feel at impact. The Babolat Xcel 16 660' is as close to natural gut as you can get from a synthetic string. Increased elasticity of the fibers provides optimal comfort and improved tension maintenance. Multifilament synthetic string.