U2 and Z2 are similar, except that U2 is pure wood and Z2 is soft carbon.
However, if we continue to compare, it should be that the surface of U2 is relatively hard, hitting the near station and the near station, followed by z2, and adding carbon can hit the far station.
Then there is the conditional theory:
If it is the hardness of the surface, mc-2 will be a little harder because there are crystals on the surface. But the bottom strength is Z 1, which is better.