One of the most frequently asked questions when consumers are buying a new mattress is "how long will this mattress last" and even though this is one of the most important parts of the value of a mattress purchase there are very few sources of information that will provide a reliable answer to this question.
When you sleep on a mattress the upper layers will compress and deflect more than the deeper layers or components partly because the upper layers are usually made to be softer than the deeper transition and support layers or components of a mattress (and firmness/softness is also a factor in the durability of a material) and partly because they are closer to the sleeping surface and subject to direct compression without any of the layers above them absorbing some of the compression forces first. It's this constant compression and deflection of the materials and components in the upper layers of a mattress that leads to changes in firmness or thickness which affects comfort, pressure relief, and the ability of the materials and components to support the weight of the body with the spine in its natural alignment.
Most materials and components will become softer as they break down over time (especially under the heavier parts of the body such as the hips/pelvis) while fiber materials will compress and pack down and become firmer and less "fluffy" over time. This is why the durability of the upper comfort and transition layers (the top 3" to 6" of the mattress) are especially important when you are assessing the durability and useful life of the mattress as a whole because they will usually be the weakest link in the mattress in terms of durability and the materials and components that are closer to the bottom of a mattress (the support core of the mattress) won't normally be the weakest link in the mattress.
Durability will also be affected by the body type of the person that sleeps on it because higher body weights (or more specifically a higher BMI) will compress the layers in a mattress more deeply than lighter body types (or a lower BMI) so they will generally need more durable and firmer materials and components in the upper layers than those that are in lower weight ranges for the mattress to maintain its comfort and support for a similar length of time.
There are also many reasons such as health conditions, age, flexibility, or just normal differences between people that some people may be closer to the "princess and the pea" end of the range and are more sensitive to changes in the mattress than those that are closer to the "I can sleep on anything" end of the range that may continue to sleep well on a mattress that more sensitive people would no longer sleep well on and would need to replace.
if a mattress is close to the edge of the comfort/support range that would be too soft for a specific person when it is new then even relatively small changes in firmness may be enough to take them outside of the comfort/support range that would be suitable for them as well and the useful life of the mattress would likely be much less than a mattress that was more in the middle of a suitable comfor/support range for that person (see post #2 here)
It's also important to understand that mattress warrantines have little to nothing to do with durability. Warranties only cover defects in a mattress which are generally defined as visible impressions that are more than a specified amount when there is no weight on the mattress (normally from .75" to 2") and don't cover changes in the firmness of the materials and the loss of comfort and support which is the biggest reason that you will need to replace a mattress.
Mattress reviews will also tell you very little about the durability of a mattress because the vast majority of reviews are written relatively soon after a mattress is purchased and in most cases include little to no information about the body type or sleeping style of the person that purchased it or the materials inside it or the support system underneath it so it's not really possible to know the reasons for any issues they may be having or whether they would apply to anyone else. Outside of actual defects in a mattress (which are relatively uncommon and will generally show up in the first year) durability issues will generally take several years to show up and in many cases the mattress which is being reviewed may no longer be available several years later anyway.
In other words, because of all the many variables involved that can affect how long a mattress will maintain its comfort and support relative to any specific person, the most meaningful definition of durability is:
"Assuming that you sleep well on a mattress when it's new ... durability is the length of time you continue to sleep well on a mattress before changes in the materials and components in the mattress caused by changes in firmness or the normal wear and tear or breakdown of the materials over time lead to a loss of comfort and support to the degree that you no longer sleep "well enough" on a mattress and decide to replace it."
While there is no way to specifically quantify or predict how long any mattress will maintain it's comfort and/or support for any particular person for certain 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 it is no longer suitable or comfortable for them (because this is the only real measure of durability or the useful life of a mattress that really matters) and because there are too many unknowns and variables involved that are unique to each person ... if you have confirmed that it meets the minimum quality/durability specifications relative to your BMI that are suggested in these guidelines 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 than the minimum guidelines suggested in this article like latex or higher density memory foam or polyfoam (in the upper layers especially) it would likely be in the higher end of the range or even longer and the chances that you would have additional "bonus time" beyond that would be higher as well.
In order to make a reasonable assessment of the durability of a mattress and bearing in mnid that because of alll the many variables involved that no set of guidelines will be 100% accurate ... and to greatly shift the odds of buying a mattress that will maintain its comfort and support for many years in your favor ... this is how to assess the durability and useful life of a mattress based on the materials and components inside it regardless of how long the mattress has been available for sale or the name of the manufacturer on the label.
Calculate your BMI or Body Mass Index. BMI is based on your height and weight and you can use one of many online BMI calculators (such as here) to find out your BMI.
Find out information that you need to know about the materials and components in a mattress you are considering listed in order from the top down or the bottom up so you can make sure they add up to the total thickness of the mattress and nothing is "missing" (see this article which you can print and take to the store). Most retailers or manufacturers that are knowledgeable about mattress materials and components and understand the importance of using more durable materials and components in a mattress will be happy to provide you with this information because it will differentiate their mattresses from the majority of mattresses in the industry that use less durable materials. If for any reason a retailer or manufacturer is either unwilling or unable to provide you with the specific information that you need to identify any lower quality materials or weak links in the mattress then I would assume that it contains lower quality and less durable materials and I would pass the mattress by because in terms of durability it would be risky purchase.
Many mattresses use foam or fiber materials that are quilted to the cover that can soften the "hand feel" or surface feel of the mattress. The quilting process will compress the quilting materials and improve their durability so as long as there are no other lower quality or unknown quality materials in the upper layers of the mattress and the quilting material is "about an inch or so or less" (in practical terms I would use 1.5" as a maximum in a quilting layer) then the quilting layer won't have a meaningful effect on the durability or useful life of the mattress so it's not necessary to find out any additional information other than the type of material and the thickness of the quilting layer.
If there is a lower quality or "unknown quality" material in the upper layers of a mattress other than the quilting layer and there are no other lower quality or unknown quality materials in the upper layers of the mattress (including any quilting layers) then as long as it's only an inch or so or less then it also wouldn't have a meaningful effect on the durability or useful life of the mattress so once again it wouldn't be necessary to find out any additional information other than the type of material and the thickness of the layer.
There are many different names that are used in the industry for the same type of material so here is a list of the most common materials that are used in mattresses so you can identify the type of materials and components in the mattress regardless of the name that any specific manufacturer may use.
Materials and components that can have a significant effect on the durability or useful life of a mattress depending on their quality/density or thickness:
Polyurethane foam (often called polyfoam)
Memory foam (or gel memory foam)
Natural fiber batting (cotton, wool, silk, horse hair)
Semi synthetic fiber batting (rayon made from bamboo or other cellulosic materials or PLA made from corn starch, tapioca roots, or sugarcane)
Synthetic fiber batting (generally polyester fibers)
Firm densified polyester fiber
Materials and components that are all high quality materials that are very unlikely to reduce the durability or useful life of a mattress:
Latex foam (either Dunlop or Talalay made with natural rubber or synthetic rubber or a combination of both)
Soft solid gel layers (where the gel isn't mixed inside a foam material)
Buckling column gel
Microcoils or mini coils (thinner versions of pocket coils that are used in comfort layers instead of the support core in a mattress)
Innersprings (Bonnell coils, Offset coils, Continuous coils, or Pocket coils used as the support core of a mattress)
Once you know the type and thickness of all the layers and components in a mattress then you can identify whether the mattress has any lower quality materials or weak links that can compromise the durability and the useful life of the mattress by comparing them to the following guidelines.
If your BMI is less than 30:
Polyurethane foam (often called polyfoam): If your mattress is one sided then I would make sure that the density of any polyfoam is at least 1.8 lb per cubic foot or higher. If the mattress is two sided then I would use a minimum density of 1.5 lbs per cubic foot or higher.
Memory foam (or gel memory foam): If your mattress is one sided then I would make sure that any memory foam is at least 4 lb per cubic foot. If the mattress is two sided then I would use a minimum density of 3 lbs per cubic foot.
Natural, Semi Synthetic, or Synthetic fibers: Fiber materials are usually used as a quilting material in the cover and will tend to pack down and form impressions to some degree over time (although these will also tend to even out as you sleep in different parts of the mattress) so I would tend to make sure that any fiber layers are only "about an inch or so or less" (again in practical terms I would use 1.5") to minimize any impressions in the mattress to a level that won't have a meaningful effect on the comfort and support of the mattress.
Firm densified polyester fiber: This is often used as a foam substitute because it is even less costly than polyfoam (which in turn is less costly than specialty foams such as memory foam or latex) and you will generally find it in low budget mattresses or in institutional mattresses where cost is a more important consideration than durability. I would avoid any mattress that uses more than an an inch of this material in the upper layers but it can sometimes be found as a stabilization layer in the bottom of a mattress under an innerspring support core where it will have much less effect on the durability or useful life of the mattress and would be appropriate as a "cost/durability" compromise" for a mattress that is in a lower budget range.
All the other materials and components on the list: These are all durable materials and components that wouldn't be a weak link that would compromise the durability or useful life of a mattress.
If your BMI is 30 or higher:
Higher BMI ranges will need more durable materials and components in a mattress and in a BMI range of 30 or higher I would include any 1.8 lb polyfoam or 4 lb memory foam as a "lower quality/density" material (relative to a higher BMI only) and minimize their use to a total of "about an inch or so or less" in the mattress.
Polyurethane foam: If your mattress is one sided then I would look for 2.0 lb per cubic foot density or higher. If the mattress is two sided then I would use a minimum density of 1.8 lbs per cubic foot or higher.
Memory foam (or gel memory foam): If your mattress is one sided then I would make sure that any memory foam is at least 5 lb per cubic foot. If the mattress is two sided then I would use a minimum density of 4 lbs per cubic foot.
If your BMI is 20 or lower:
In lower BMI ranges then using slightly lower quality/density and less durable materials can be a little less risky because you won't sink into the mattress as much and lower density foam materials won't be subject to the same degree of compression that cause them to soften and break down as quickly as they would for higher weight ranges. While I would generally use the same guidelines as for a BMI that is less than 30, if you are restricted to lower budget ranges where higher quality materials may not be available (say under $400 or so) and if there is a lower quality/density layer that is deeper in the mattress and has an inch or two of higher quality and more durable materials above it then a slightly lower minimum guideline of 3 lb per cubic foot density for memory foam or 1.5 lb per cubic foot density for polyfoam may be worth considering as a reasonable "cost/durability compromise".
NOTE: I have recently switched to using BMI rather than weight so in many of the previous forum posts where you see "higher weight ranges (more than the lower 200's or so)" I would use a BMI of 30 or more and where you see "average weight ranges (lower 200's or less)" I would use a BMI of less than 30.
Other factors that can affect the durability and useful life of a mattress:
Firmness: Firmer materials will tend to compress less and last longer than softer versions of the same material so if you are choosing between two mattresses that are both a suitable choice in terms of comfort, firmness, and PPP and one of them is slightly firmer than the other and there are no other significant differences between them that would affect durability then I would choose the one that is slightly firmer.
Quilting layers: Foam or fiber that is quilted to a cover will be compressed by the quilting process and would be more durable than the same material that isn't quilted to a cover.
Inner tufting: Inner tufting is a method of construction that secures the layers and components in a mattress together by compressing the mattress and using a cord or tape that goes right through all the layers of a mattress at regular intervals and is secured or anchored on either side with some kind of padded button or felt washer. It pre compresses and holds all the layers and materials together and prevents shifting and gives the product the unique tufted look, will create a firmer mattress, and will greatly increase the durability of a mattress even if it uses materials that would otherwise be a weak link and reduce the durability or useful life of the mattress if they weren't tufted.
Layer position: Deeper layers or components are less subject to compression forces than layers that are closer to the surface so if you need to make any compromises in the quality and durability of the materials in a mattress because of a restricted budget then lower quality and less durable materials that are deeper in the mattress would have less effect on the durability and useful life of a mattress and be less risky than the same layers that are closer to the sleeping surface.
Convoluted layers: Convoluted layers are less durable than a solid layer of the same material so if there are convoluted foam layers in the upper layers of a mattress and the material is also at the minimum density range for your BMI then it could have some effect on the durability and useful life of the mattress and I would lower your expectations slightly. I would also make sure that there isn't more than one convoluted layer. If the convoluted materials are higher quality and more durable than the minimum guidelines for your BMI then it wouldn't be an issue.
One or two sided: Assuming that you flip and rotate it on a regular basis (see post #2 here) ... a two sided mattress will be more durable than a one sided mattress that uses the same comfort layers and components on only one side of the mattress. There is also more about the pros and cons of one sided vs two sided mattresses in post #3 here.
Replaceable layers: Some mattresses (most commonly latex mattresses) have individual loose layers and a zip cover where each layer can be removed and replaced. Some local manufacturers will also open up the cover and replace individual layers in a mattress. Because a mattress will normally soften and break down from the top down this can be a benefit in terms of durability because a single layer that has softened before the other layers and components in a mattress (usually the upper layer of a mattress) can be replaced without having to replace the entire mattress. A sleeping system that has a mattress/topper combination would have similar benefits that allows you to replace the topper without replacing the entire mattress.
Insulator over an innerspring: Many innersprings that have a lower coil count and are linked with helical coils (rather than having the coils inside a fabric pocket) will need an insulator above the coils to even out the feel of the innersprings and make sure that the layers above the innerspring don't compress and pocket into the innersprings which can lead to a mattress that feels lumpy. These are usually some type of non woven material such as densified or bonded polyester or cotton fibers or resinated textile clippings or coconut coir or a flexible mesh material and without this layer a mattress will lose it's comfort and support much more quickly as the padding compresses into the coils. Mattresses that use pocket coils with a higher coil count that are surrounded by a fabric don't generally need an insulator (although some may still have one) to prevent the padding materials from pocketing into the coils.
Foam surround: Many innerspring mattresses have an edge support system to create a firmer edge for those that tend to sleep with most of their weight concentrated on the outer few inches of the mattress to prevent roll off, make it easier to get in and out of the mattress, or for those that often sit on the side of their mattress. One of the methods that is commonly used for this is a polyfoam surround which glues a firmer polyfoam layer on the 4 sides and bottom of the innerspring and if you are one of those that sleep on the edge or sit on the side of your mattress on a regular basis then I would use the minimum polyfoam guidelines for your BMI for the foam surround as well.
Long term compression: If the materials or components in a mattress are sourced in Asia or China and are compressed during shipping or storage in a warehouse for more than a few weeks then the durability of the materials would be more uncertain because longer term compression can reduce the durability of the materials or components in the mattress and there would be a higher chance of experiencing durability issues over time (see post #6 here).
While I would want to know the specifics of an innerspring in a mattress to be able to make more apples to apples comparisons between mattresses and I would want to know the thickness of the innerspring so you can add up all the layers and components in a mattress to make sure that they add up to the total thickness of the mattress and confirm that you aren't missing any layers ... more detailed information about an innerspring isn't usually that important in terms of durability because innersprings aren't normally the weakest link of a mattress and will generally last longer than the padding layers above the innerspring. For those that want more information about the pros and cons of different types of innersprings for reasons other than durability there is more information about innersprings in this article and in post #10 here.
There are also other variables that can affect the durability and useful life of a material such as the specific chemical formulation of a foam material, the cell structure of the foam, or some other more "arcane" and less significant factors but in practical terms these aren't as relevant or important as the other variables that are discussed in this article which will be enough to make sure that the odds of buying a durable mattress that will last you for many years are very high.
While it's not a durability issue ... I would also make sure that the foam materials in your mattress have a reliable safety certification as well so that you can have some confidence that any harmful substances or VOC's are below the testing limits for the certification which for most people would be "safe enough" (see post #2 here for more information about some of the more reliable "safety" certifications).
It's always more realistic to think of about 10 years as a maximum 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 and more durable materials that soften, compress, or break down much more slowly is much more likely and you will find some people who have slept well on some of the most durable mattresses and materials for several decades but these are the much more the exception than the rule.