To provide a member having a strength higher than that of a lighter member.

If a high pressure is applied from inside, even a soft member, a weak member or a member with poor durability raises its durability. However, in this case, even if it becomes strong as the member, it becomes not so easy to use or come to be hard to handle and require consideration to an environmental problem or the like in relation to the use of carbon dioxide. On the other hand, making it stronger and lighter can improve it as the member or raw material.