Fiber-rush is a man-made twisted kraft paper that very closely resembles the natural rush historically used on Shaker style chairs, ladder-backs, Hitchcock and hitchcock style chairs, and others.  Any chair with four sturdy seat rails can be done in fiber.   Fiber is a much more practical alternative to natural rush for every day use and is much, much cheaper.  It is also more durable, and will last longer in constant use.  A well made fiber seat will last anywhere from 5-25 years or more, as long as you don't let your cats, dogs or rabbits get to them!  (Not so much dogs, but cats and rabbits love to sharpen their teeth and claws on this material)  I do not do natural rushing myself, but have an aquaintance who is a master rusher and will be happy to refer you to him.