Is this a product that is generally available, or is it more an idea that you've heard of but never actually encountered? If it's the first, see if you can get ahold of one to look at - see how pliable the boning is, see how firm or stretchy the fabric is, that sort of thing. If it's not really a standardized thing, you're going to have to take a look at your friend's needs - for support, mobility, etc - and try to figure out what materials will provide.