Hi joebk,
This is not as simple a question as you may think because all the layers of a mattress are affected by the layers both above and below them and the thickness of the topper also plays as big a role as its softness. The two things that will be affected by foam softening are comfort (pressure relief) and alignment (support). It is the loss of either comfort or support that is the biggest reason that a topper or a mattress needs to be replaced.
No matter what materials is used in the top layers of a sleeping system (whether it’s a topper, a pillowtop, or the comfort layers) … they will degrade faster than the lower layers. If they are a foam … they will soften. If they are a fiber, they will compact and become firmer. the deeper in a mattress a layer is … the more slowly it will lose it’s original properties.
So if you have a topper that softens and it is fairly thin … then it would allow you to “go through” it more easily and you would feel more of the layers below it. If the deeper layers were firm … you would feel more firmness and if they were very firm … it would feel more like “bottoming out” (sleeping on a layer that wasn’t providing the pressure relief you need). In this case … foam softening would result in a mattress that felt firmer. If the topper was thicker … then as it softens it may still “hold up” the lighter parts of your body without reaching the firmer layers below them but the parts of the thicker layer under the heavier hips and pelvis would soften more rapidly and sink in more so you would end up with an alignment issue (the hips/pelvis was sinking in too deeply relative to other areas of your body) even though the pressure relief may still be fine.
Foam of all types will go through 3 stages of softening. The first stage is the initial break in period where the softening is more rapid (first 90 days or so). For some people this initial softening period can lead to a degree of softening where they lose comfort or alignment (especially if they made a choice which was close to the limit of softness that was suitable for them when they first purchased the mattress). This initial softening is followed by a more gradual softening over a much longer period of time. The final stage is where the foam loses it’s resilience and breaks down and begins to show impressions that don’t come back when there is no weight on the mattress.
High quality memory foam (such as 5 lbs or more) is in the same general range of durability as HR polyfoam and latex is more durable yet. This is assuming an apples to apples comparison because softer foam on top will also break down faster than firmer foam because it is subject to more mechanical compression.
The other challenge with memory foam though is that there are so many different types (as you can see in post #9 here and post #8 here which talk about the many different properties of different memory foams). Memory foam also has a quality called “creep” which means that like any material with viscoelastic properties you will continue to sink in deeper over time as the foam relaxes. HR polyfoam and latex is more consistent between different manufacturers with similar specs and has much less creep (the compression that you start with will be similar to how you wake up). It is easier and less “tricky” to make the most appropriate choices with more elastic foams (polyfoam and latex) than choosing viscoelastic foams in other words. Of course being a little more “tricky” to make a good choice doesn’t mean that it is a bad choice either … there are just more things to take into account.
So just to re-affirm the earlier part of this post … memory foam as a material doesn’t have a shorter or longer life than polyfoam because it depends on the density/quality of each you are comparing and on the rest of the layers in the sleeping system. Good quality memory foam will be roughly equivalent in durability to good quality polyfoam and both will be less than good quality latex.
Again … this will depend on the layering in the sleeping system as a whole, the thickness of the topper, the quality of the topper, and what is under the topper more than just the topper by itself. Different combinations can lead to either the loss of comfort and support even with high quality more durable materials if the combination of materials you use has little “room” for foam softening. In an appropriate combination of layers that is more in the “middle” of your range or is even on the firm side … the sleeping system as a whole will last much longer. The advantage of a topper as well is that once you make a choice that “works” for you … then it’s easy to replace the topper with a similar one because you already know what type of topper works for you and the topper will extend the life of the materials below it.
In looking through your choices I would ask the manufacturers about the quality of the specific foam they offer. The “accurate” definition of HR foam (which has both a higher density and better performance properties than conventional foam) is that it is 2.5 lbs or higher, has a compression modulus (also called sag factor) of 2.4 or higher and has a resiliency rating of 60%. There are many foams that are labelled as HR which don’t have all these specs. There are also foams that are “high performance” foams that have a higher sag factor or higher resilience that don’t meet the density requirements of HR foam (they are often called “high comfort” foams or “high performance” foams).
In addition to this … ILD (or the term which replaced it called IFD) is a measure of the softness/firmness of the foam which has little to do with its density. Both higher density foams and lower density foams can be made in a wide range of firmness choices. The choice of firmness would be part of making a suitable choice for your needs and preferences and would be based on the overall design of your sleeping system. Generally the top few inches would be softer, the middle layers would be a “transition” zone which would be partly for comfort and partly for support and then the lower layers would be much firmer to “stop” the heavieer parts of the body from sinking in too far and causing misalignment. The different combinations of softness/firmness levels of these three vertical sections of a mattress and how they interact together is the “art and science” of mattress construction and fitting a mattress to the different body types, sleeping positions, and preferences of different people. Most people who have been making mattresses for decades will tell you they are still learning as new materials emerge and new ideas about how to design a mattress become more popular.
The Albany Foam choice has the density of HR foam (and probably is) but the ILD (35 lb) is on the firm side for a comfort layer.
Neither of the Foam Products choices are HR foam. The 1520 means it is 1.5 lbs density and has an ILD of 20 lbs. The 2030 means it has a density of 2.0 and an ILD of 30 (which is also on the firm side for a comfort layer depending on body type and sleeping position).
The Foam Order foam descriptions are here and you can see that the Everflex V 34 is 2.6 lb (HR range) and has an ILD of 34 as you mentioned. They consider this to be a very high quality foam that will last 15 years (but it will depend on the factors that I mentioned earlier whether it will last 15 years for you). The Duraflex is what they call “mid grade” (this is relative to their other foams) but some foam suppliers would consider this high quality compared to other lower density foams they supply. For most people … 34 ILD is on the firm side but this is personal preference and depends on thickness as well. To know whether it worked for you would require a personal reference point of testing a mattress where the ILD of the foam layers were known. Without this reference point … a conversation with a more knowledgeable foam supplier that included the layers that the topper was being used on would provide your best guidance. They know the properties of the foams they sell better than anyone (hopefully).
Foam Online has the HR foam and the Evlon which is a higher density version of HD foam. Both of these are more in the range of “soft” that most people would prefer.
With a1foam and fabrics I would confirm the density of the foam because many foam suppliers call a foam HR when it’s not and they mean it in a more “relative” way (higher density than other foams they carry) instead of meeting the specs of actual HR foam. It is also in the “soft” range that most (but not all people) would prefer but again this depends on what is over and under it and on the thickness of the topper.
The bottom line is that without a reference point of foams that you have tried and know the specs of the layer … the guidance of the people selling the foam would likely be the most accurate means of making a choice rather than trying to decide by “specs” that have little meaning to you without the personal experience of actually lying on a mattress with specs that are known.
I would tend to keep it simple and go with a “soft, medium, or firm” rating which is likely to be close enough for what you need, stick with the thinnest layers that you believe would do the job, and buy the best quality that you can reasonably afford whether it is memory foam, polyfoam, or latex (or even other choices such as wool).
After knowing all of these more “complex” more technical factors that are in the first part of this post … I would tend to take a different less “spec” oriented approach to your topper and first try to describe as accurately as possible what you are feeling on the mattress now (in terms of alignment and pressure relief) and how you would like it to feel.
The first step would be to identify what you are looking to achieve in the overall feel and performance of the mattress and topper as a whole. I would try to describe this in more specific terms such as are you looking for better pressure relief, how is the support and alignment, and which specific areas of the body are you having issues and what are the actual “symptoms” involved. I would try to identify and quantify as much as possible how much of a change you need (are you close or far away from your ideal).
The next step is to decide between your preference of slow response or fast response materials. This is a personal preference and should be based on testing both in stores to see which you prefer.
The next step is to identify what is in the mattress you have (which of the Ikeas did you buy) so that you can make less “risky” choices in terms of how much soft foam will be in the upper layers of the sleeping system.
Once you have done these three steps … then you will be in a better position to talk with the suppliers of the topper you are adding and make the choice of the softness and the thickness of the topper in the type of material you prefer based on your body type, sleeping style, personal preferences, and the layering of the mattress it will be used on.
Phoenix