Coil spring inserts work in two ways. First, inserts work by changing the structure or anatomy of the spring itself. The insert changes the spring from a single spring, to two separate functioning sections. This split increases your coil capacity because it generates additional stiffness. In theory, you could shove a piece of wood in the middle of a spring and you would see increased capacity. So, yes, Coil SumoSprings are the same as other inserts, wood included. So what makes one insert better than the others? Second, the spring rate of the insert’s material affects the spring’s behavior. The block of wood has no spring rate, so although you may see an increase in capacity, it is solely because you made the springs stiffer. By using micro-cellular urethane, the Coil SumoSprings act as a spring within a spring. Not only is capacity increased by the change in spring structure, but the progressive spring rate of the Coil SumoSprings increases capacity and ride comfort as well.