It is not steel boned, but is is pretty stiff, so I am ok with it.
I wear a size 12/14, I needed to buy the 3XL.  When it says measure yourself, take heed!  I had to measure based on my waist, not my bust.  I require "help" to boost the girls up, but my waist is definitely looking the way it is supposed to.
The belt is a BOO for me, it doesn't have enough holes for is to lay low on my hips, like on the picture, though it will sit at my waist.
The bolero is unattached and sits weird on me, with a rather large gap between the shoulder blades, even with it laced up real tight.  Though from the front, it looks fine.