This is a neoprene neck piece that i made for my own costume fit test. It is held on with a magnet and cloth but can use a better system. It looks and fits great though! My neck is 13" around but the flex can allow slightly larger sizes.

The piece was sculpted in wax clay and cast in neoprene aka synthetic latex rubber...but is safe for those with latex allergies. You can read more about it here! http://creaturecastrubber.com/

These pieces are flexible but durable and very lightweight. They can be painted with acrylic paint and sealed. They can also be drilled into or dremeled. You can even use leather rivets on it! I think of this stuff sort of like tough leather once is is fully cured, it behaves very similarly. I have also used high heat hot glue to affix things to it ( score the surface first!) . I would recommend that you store the piece so that it is not crushed to prevent it from warping but if it does, it can be set back to its normal shape. These will require some edge trimming, easily done with scissors or dremel.