when comparing all latex mattress vs a latex topper with high quality polyurethane…what are the main differences? longevity? softness?
there is definitely a cost difference but if it is high quality polyurethane underneath will it matter as much?
is there any science with the 3 or 5 zone for mattresses? Should it be firmer underneath your hips? or firmer under your head etc?
looking into getting my first latex or latex+foam mattress and nervous about the decision
Hi disellusional,
Welcome to the Mattress Forum! 
[quote]1) when comparing all latex mattress vs a latex topper with high quality polyurethane…what are the main differences? longevity? softness?
there is definitely a cost difference but if it is high quality polyurethane underneath will it matter as much?[/quote]
A latex support core is more durable, more resilient, more elastic, more adaptable to different weights and shapes and sleeping positions, more supportive (it has a higher compression modulus so it gets firmer faster with compression), more “natural”, and has a different more “springy” and responsive feel than polyfoam. It is a higher performance material. Of course it is also more expensive than a polyfoam core and for some people … a latex hybrid which has the benefits and “feel” of latex in the upper layers (the top 3" - 6" which are the most subject to wear and tear and contribute more to the overall “feel” of a mattress) is worth the cost tradeoff. For others it isn’t. All of this though is to make clear that they are not comparable in overall performance terms.
Ultimately, the compression of each layer (mainly controlled by thickness, firmness, compression modulus, hysteresis, and position along with a few other specs) are what creates the pressure relieving cradle of a mattress in the top layers which re-distributes weight and pressure on the bony prominences and pressure points of the body while the resistance to further compression of the deeper layers is what “stops” the heavier parts of the body from sinking down too far and putting the spine and joints out of their natural alignment. The balance between the opposing needs of pressure relief and spinal alignment is the main factor behind all mattress design and theory and why different mattresses match the body types and sleeping positions and preferences of different people … or don’t.
There is no formula that can predict with any certainty what type of layering you may do best with that can possibly be more accurate than your own personal experience and without this the next best way to decide on the design of a mattress is to use the “averages” of a manufacturer for people of your weight range, body type, sleeping style, and personal preferences. These “averages” may vary from manufacturer to manufacturer depending on the specific designs and options that they have available (including all the components such as the cover or quilting layers which can also have a significant effect on how the mattress feels and performs not just the latex or foam layers).
Various zoning systems can be very useful and worth considering for people who have more challenging circumstances or sensitivities, body types that are more difficult to “match” to a mattress, more complex medical issues, or who have a history of having more difficulty in finding a mattress that works well for them. There is more about zoning in this article and in post #11 here. You may also want to read post #2 here and post #7 here (latex monozone unique properties).
Phoenix