The combination of different materials were selected for strength and flexibility, difficult to break and the ability to return to the original form without having to increase the size of the cross-section.
-異なる素材の組み合わせることで、断面積を大きくする事なく、良く撓り（しなり）折れにくく、元の形状に戻るという条件を満たすよう工夫された。