Not sure what the material is called, but it appears to be the same stuff that's used on the connector pieces on the fast pack accessories. It's a plastic with some flexibility to it and a bit of softness, but definitely not PVC. This being my first Yamato Valk purchase, I was very leery given the past problems of breakage that Yamato's had in what seems like all their transforming toys, but I've been very pleasantly surprised at the durability of the figure. Saying that, I'm a collector who is used to handling figures somewhat delicately. I never force a movement, and if something seems like it's not right, I go looking at the manual first.
Anyway, mine seems just fine and unlikely to break.