Hi magpie,
The upper layers or quilting materials in a mattress aren’t really for support (which comes from the deeper layers in a mattress) but more about the “feel” or pressure relief of a mattress. There is more about quilting materials in post #12 here and the posts it links to and there is more about the differences between primary support, secondary support, pressure relief, and “feel” in post #4 here.
The “art and science” of mattress design can be very complex and it can be difficult to predict the effect of a single component or material because all the layers and materials in a mattress will affect all the other layers and materials in the mattress and there are many versions of every type of material that can also make a significant difference so it’s generally much easier to test a mattress and use your personal experience on the “combined effect” of all the layers and materials to decide whether a mattress is a good match for you in terms of PPP rather than trying to predict the effect of any individual material or component.
There are many mattresses that use synthetic polyester fibers as part of the quilting layers so it’s not at all unusual to find these in a mattress.
Phoenix