HEAD YOUTEK Six Star Racquet Unstrung tennis racquet d3o integrated in the lay-up and positioned in the shaft area where the racquet flexes the most On high-speed impacts, d3o molecules lock together to increase racquet stiffness for maximum power; on low-speed impacts, the molecules absorb impact to provide a softer touch for better feel Head Grommets with Teflon friction-reducing polymer create a self-lubricating effect in the base material, allowing the strings to slide through the grommets with nearly no friction for less energy loss and more power QuadFace extends the stringbed at key points of the frame, providing longer strings and an enlarged sweetspot for maximum power