Hi EPmattresshunter,
Both polyfoam and latex come in a very wide range of firmness levels so any differences in firmness would depend on the specific firmness of the layers you were comparing. Outside of any firmness differences between one or the other … the main differences would be in how the different “properties” of each material feel to you which in turn would depend on the position of the layer in the mattress, the thickness of the layers above it (and the thickness of the layer itself), na on the body type, sleeping style, and sensitivity of the person on the mattress (heavier body types or side sleepers will compress the top layers more so they may “feel” some of the deeper layers more than those that are lighter or sleep in other positions).
If the polyfoam is a higher density version and is deeper in the mattress then it would make much less difference in terms of durability (see the quality/durability guidelines here).
None of their mattresses have any lower quality materials or “weak links” in their design.
Phoenix