Beaver tail is stiff and durable.
When commercially tanned it can be more pliable.
I like to back it up with suede or light leather but it is easy to work with and reasonable to buy.
The tails I have are from beaver I had trapped years ago, sold the hides, saved the tails and tanned them.
I bought a beaver tail wallet that was crafted by natives and that's when I realized the tails could be put to good use.
They are usually left on the carcass and discarded.
Kevin.