Hi Vicky,
While the “S” brands are among the least transparent when it comes to disclosing the quality/density of the materials in their mattresses … they certainly aren’t the only ones that don’t disclose what I would consider to be essential information that is necessary to make an informed purchase choice (see this article for my transparency “ratings” of the top 15 manufacturers).
While some information can legitimately be considered to be proprietary to a manufacturer … there are many manufacturers that claim that the information you would need to make an informed choice is also somehow “proprietary” but I certainly wouldn’t agree. You can read a little more about “so called” proprietary materials and using this as a justification for not disclosing what I would consider to be essential information here and here and here.
Phoenix