Hi Lady G,
All of the different types of buckling column gel are made by Edizone and licenced for use by different manufacturers so it would be more accurate to say it was required “by license” than “by law”. Edizone doesn’t release the proprietary information about the specific differences between them but the Orthogel for example does use a foamed material inside it (see post #7 here).
They are all very durable materials with the same basic function but they will have a different buckling threshold and have a slightly different feel between them depending on the version and design and on the other layers that are either above or below them. Forum search on Edizone or on Intelligel and Orthogel and Somnigel (you can just click the links) will bring up more information and some feedback about them as well.
Phoenix