Hi kdreams,
The durability of the materials in a mattress and their relationship to the durability and useful life of a mattress can be a complex question and is relative to the individual needs and preferences of each person but I think the best definition for durability I can come up with would be …
“How long does a mattress remain suitable for the comfort and support needs and individual preferences of a specific person”.
The loss of comfort (generally pressure relief) and support (spinal alignment in all your sleeping positions) is the biggest reason that most people need to replace a mattress and when this happens would be different for different people. A mattress that still provides good comfort/pressure relief and support/alignment and is still perfectly suitable for one person may be well past its due date and no longer provide comfort and/or support for someone else so durability and the timeframe when someone crosses the thresholds from “sleeping well” on a mattress to “sleeping OK” to “tolerating it” to experiencing more significant symptoms of pain or discomfort and deciding to replace it can vary with each person and can be very subjective.
Having said that … there are clear differences between the durability of different materials and mattresses and there are many factors involved that will affect how long one mattress will last relative to another one. There is more about the different factors that can affect durability and the useful life of a mattress in post #2 here.
Some relative comparisons of different materials and components are in post #3 here.
There is also more about how the suitability of a mattress choice and the sensitivity of each person to a range of comfort/pressure relief and support/alignment can affect the useful life of a mattress for each person in post #2 here.
What this means is that a mattress will generally have to be replaced long before the materials themselves have completely worn out or broken down because foam softening and the breakdown or permanent compression of the materials or components in a mattress will have different effects on different people and any specific estimates for any particular person may be a “rough guess” at best. What can be said with certainty is that higher quality materials that soften or change more slowly will maintain their comfort and support and last longer than lower quality materials that soften or change more rapidly, latex is the most durable of the different types of foam materials, higher density memory foams and polyfoams will last longer and maintain their properties longer than lower density foams of the same type, and that the layers both above and below any specific material or component in a mattress will affect the durability of that material as well.
While the latex in a core layer is a more durable material even than good quality polyfoam or an innerspring, since the core layer is less subject to mechanical compression than the upper layers and are generally firmer (firmness is a durability factor) they will last longer than the same materials used in the comfort layers. To the degree that you are compressing the support layers “through” the comfort layers … the latex will be more durable than polyfoam but neither is likely to be the weak link of a mattress in most cases.
Besides a potential increase in durability to differing degrees (depending on the person and the layers over it and how much it is subject to repeated compression) … the biggest benefit of a latex core is performance and it will feel and perform differently from a polyfoam support core. You can read more about this in post #2 here.
While there is no way to know for certain how long any mattress will last or maintain it’s comfort and/or support for any particular person or how long it will take before they cross the thresholds between sleeping well on a mattress to sleeping “OK” to tolerating a mattress to finally deciding to replace it because there are too many variables involved that are unique to each person … if a mattress is well inside a suitable comfort/support range and isn’t close to the edge of being too soft when it is new and meets the minimum quality/durability specs that are suggested in the guidelines here then it would be reasonable to expect a useful lifetime in the range of 7 - 10 years and with higher quality and more durable materials like latex or higher density memory foam or polyfoam (in the comfort layers especially) it would likely be in the higher end of the range or even longer.
It’s always more realistic to think of about 10 years as a reasonable expectation for any mattress no matter what the quality or durability of the materials and then treat any additional time after that as “bonus time” because after about 10 years the limiting factor in the useful life of a mattress will often be the changing needs and preferences of the person sleeping on the mattress and even if a mattress is still in relatively good condition after a decade … a mattress that was suitable for someone 10 years earlier may not be the best “match” any longer.
Having said that … if a mattress only uses the highest quality and most durable materials and for people whose needs and preferences or physical condition or body type hasn’t changed much over 10 years then “bonus time” or even “extended bonus time” with more durable materials such as latex, higher density memory foam or polyfoam, natural fibers, or other high quality materials that don’t soften or break down prematurely is much more likely and you will find some people who have slept well on their mattress for several decades but these are the more the exception than the rule.
Phoenix