Tecnifibre X-Code H.D. blends the elasticity and comfort of polyurethane with the crisp and controlled response of polyester. Unlike a stiff polyester monofilament, X-Code HD is a multifilament made with flexible polyester fibers. This gives it a softer and slightly more muted feel than traditional polyester strings. Strung below midrange tension, our TW playtesters found this one to have a fairly soft feel straight out of the package. We also found this string to provide a little more pop than a traditional poly, while still offering plenty of control (and impressive spin!) on big swings. Using multifilament technology, X-Code is the missing link between polyester monofilaments and premium multifilaments. This is a great option for players who want the control and durability of polyester in a slightly more arm-friendly package.