Hi qazy,
Yes 3-4 lb density tends to be for memory foam and not the polyfoam core of a mattress.
Regarding specifically cotton-silk-cotton, there isn’t just one type of this mattress pad or protector, so it would come down to the blend, weave and overall quality of the fibers being used. Silk can be a very durable natural material that can be quite “cool” sleeping, but again that is very subjective and I don’t delve into the specific details of all of the protectors and pads out there, as that would be an entirely new forum, and I already have my hands full with this one!:lol:
There is a thread here that speaks to sheets and within that thread there are quite a few links and I do speak to silk a bit, and you may find the information there interesting. I think you’d want to first decide if your desired some sort of a mattress pad or a true protector (waterproof) and then move onto the materials you find in the items in the specific category you choose.
Phoenix