Hi needhelp,
Many manufacturers keep the source of their materials confidential for competitive reasons and don’t disclose this to their customers but they could certainly provide the type and blend of any latex in their mattress which is the information that would be important to know.
Both manufacturers of Talalay latex (Latex International and Radium) make two basic versions. One is 100% natural (it has no synthetic rubber in the formula) and the other is a blend which is approximately 30% natural rubber and 70% synthetic rubber (although it can vary to some degree). They will tell you which one they use but I believe it’s the blended Talalay. There is more about the different types and blends of latex in post #6 here.
Softness and firmness are very subjective and relative to each person’s perceptions. In a comfort layer 28 ILD would usually be considered medium but 28 ILD would be on the softer end of the range if it was used as a support layer so softness/firmness also depends on the function of the specific layer.
If you have tested a specific combination then you can use your testing to decide if you need more support or more pressure relief than the mattress you are testing and use this as a reference point for any changes to the mattress. If a manufacturer can also make changes to the mattress after a purchase then you can also use your own actual sleeping experience to confirm that the design is suitable for you so knowing the options you have after a purchase can also be an important part of your research and your personal value equation.
Phoenix