There is a lot of misinformation out there on the interwebs about spiral steels, so please allow me to clear the air: while a fantastic option in certain circumstances, they are not objectively better than flat steels.
Spiral steels are named such because they are literally comprised of tiny flattened spirals, as opposed to flat steels: a solid piece of steel. Spiral steels are very flexible, making them an excellent choice for fashionable burlesque dancers, trapeze artists, contortionists, and other performers for whom range of mobility is of upmost importance.
While the flexibility of spiral steels is a boon, the fact that they can’t support the form in the same way flats do is a bust. I have corsets for daily wear made with both and frankly, sometimes I prefer the structure and support of the flat steels. However, the spiral steels are more forgiving on my ribs as I drive on long commutes. There are definitely reasons to have both varieties in your corset wardrobe, but the fact that some corsetiers are purporting that one is infinitely better than the other for all occasions is absurd.
Unless you are a tiny acrobat person, spiral steels may not be for you. Corset size 26″ and up would need extra bones put in if they wanted spiral steels, simply due to the fact that the ultra bendy bones would eventually flare out of shape unless they had some back-up (it’s not you, darling. You are perfect the way you are. It’s the bones).
Another hazard is that the spirals get kinks in them all too easily. Bend over to tie your shoe too quickly? Pick up a lucky penny too excitedly? You’re fucked. Terror strikes in my heart whenever I carefully lean over in my spiral steeled corset for this reason.
I love my spiral steel corset! But it was definitely a considered choice when I had it made for me. So don’t get scooped up in the verbiage some corsetiers will feed you about the all-reaching superiority of spiral steels that they use exclusively in their fashions. Variety and options are better, right?