The D30 protective inserts at the heart of Fox Racing's Launch Pro D30 Elbow Guard solve the dilemma of padding vs flexibility. D30 is a wacky polymer that is flexible under slow, non-calamitous energy inputs--think bending your elbow. Under the shock of sudden impact, though, the material stiffens to absorb and diffuse energy before returning to its pliant, non-impact form. We know that all sounds too good to be true, but, well, it's true. The stuff works. And in order to keep it working through multiple impacts and seasons of abuse, Fox shields it with an abrasion-resistant, replaceable cap.