Help making a Collar

[CosplayWho]

Hello, so I am attempting to make Shiros collar from Deadman Wonderland:

Reference:
http://moarpowah.com/wp-content/uploads ... /Shiro.png
+
http://geekrevolt.com/wp-content/upload ... on-top.jpg
+
http://www.zerochan.net/591704#full

So I have tubing for the top and bottom rings. However I have no clue what I should do for the middle.... I have tried craft foam, but I can't get the shape I am looking for... It won't bend in the middle like its shown in the pictures. So I guess my question is what materials should I be using and how should I use them. I am new to cosplay and any advice will be greatly appreciated. Thanks in Advance.