I am often asked which and how much boning I recommend for a given figure. The answer depends on many parameters, so I have created an extra page such as not to clutter the instructions pages.
When choosing the type and amount of boning it is important to understand how stays "work". It is a common misconception that corsets or stays can compress the body as if it was a sponge. That's not possible, though, because the body, unlike a sponge, isn't full of air that can be queezed out: It is chock-full of bones and organs. Whatever space it occupies is needed - all of it. So if you want to make a waist narrower, you can only do so by pushing the body mass somewhere else. Think of a baloon: If you squeeze it in one place, it bulges in other places.
In case of a very slender figure, you may be able to relocate the inner organs a tiny bit before the bones (that is, the ribs) put a stop to it. In case of a "stout" figure, on the other hand, there is a lot of body mass on the outside that can be relocated so that a corset can be much more effective - if it is properly made.
Someone with a normal figure (US size 12-16, no handicaps) should not have any problems with stays; the rules-of-thumb given in the instructons should suffice both for boning strength and amount. People wearing smaller sizes may find stays uncomfortable because the pressure almost directly works on the bones, but the type and amount of boning is the same as for normal figures, or a little less of it.
It gets more complicated for non-standard figures: hollow backs, hourglass, fat or well-endowed. This is what the rest of this article is about. Anyone not afflicted by any of those features may safely return to the instructions pages.
Extreme hip-to-waist or breast-to-ribcage ratios as well as the curve between a hollow back and the bottom require special boning. If a "stout" figure is laced into a corset, all of the three aforementioned issues tend to combine. In all those cases, half-boned stays are not recommended. The following therefore assumes fully-boned stays.
Whenever there is a sharp curve from wait to hip or from (hollow) back to bottom, plastic boning alone is not enough: Even if the stays are fully boned, only 2-5 bones run through into the tabs, so they cannot properly support each other. If the tabs are spread very wide, they may stand out almost vertically, i.e. they are bent sharply. After a while, the plastic will suffer from material fatigue, i.e. like a rubber band that has been overstreched, it will refuse to return to its original shape. The boning will then be unable to take pressure away from the waist as it is meant to do and it will become painful.
Use steel boning of the same width as the plastic to prevent this: Steel doesn't bend as and therefore doesn't fatigue as easily as plastic does. If you have wide hips, use one (two in extreme cases) steel bone per tab around the side. For a hollow back, one per tab around the back. If you're fat, one or two around the sides and back. If you're well-endowed, fully-boned should be enough, but if you want to be on the safe side, use steel in every fourth tunnel around the front.
Steel boning of 0,5x5 mm is more rigid than 1x5 mm plastic boning.