X-Formula (XF) is another industry leading innovation from the Bones Wheels factory. X-Formula rolls over rough terrain like softer wheels do, but slides much like a harder wheel will. X-Formula rolls much smoother and faster on all terrains because it absorbs vibration and softens impacts much better than any other wheel in the market. The slide-ability comes from its unique blend of high performance materials. X-Formula will slide when you ask it to, and grip when you need it most. This is because X-Formula is specially formulated for any terrain. It has been developed over a ten year period to optimize performance and fine tuned to perfection.