Hi moose0721,
This will be a longer reply because both the question about warranties and about 4 lb memory foam and softness deserve more detailed replies because they are not as “simple” as most people would think.
Your warranty question highlites one of the major differences between manufacturers who depend on their local reputation and manufacturers who depend on their advertising. It also brings up the wonderful world of warranties themselves … and more importantly warranty exclusions.
Major manufacturers want their ownership or shareholders to be satisfied … local manufacturers want their customers to be satisfied. There is a big difference.
Warranties are very misleading and are one of the “managed perceptions” that has allowed the major players in the industry to introduce lower quality mattresses while increasing the warranty so that consumers don’t realize that they are being “misled”. This is particularly true of mattresses which use lower quality polyfoams and memory foams.
Polyurethane foam and memory foam (which is a type of polyurethane foam) … can soften beyond the point where it is suitable for sleeping on long before there will be an indentation which is deep enough to trigger a warranty claim. Even worn out polyfoam or memory foam after you have been off the mattress for a few hours (which is a requirement for the indentation to be measured by an “inspector”) will usually have enough residual resilience left to come back to a level within depth of impression that is inside the warranty exclusion. This and the other warranty exclusions (such as any type of stain on a mattress) are almost always enough for a major manufacturer to deny a warranty claim. This is why warranties always exclude what they call “normal softening” and the loss of comfort and support that goes with it. Only in the last stages of foam breakdown (or with an actual defect in the foam which will normally happen early in the life of a mattress) will there be impressions that are deep enough to be deeper than the exclusion which would be allowed for a warranty exchange (and believe me this is part of what they test before a mattress is “released” to the public).
Local manufacturers on the other hand “want” their customers to be satisfied and tend to feel much more responsible to honor a warranty claim even when they could “get away with” not doing so. They will for example often offer to rebuild a “problem” layer of a mattress at a minimal charge if the circumstances or legitimate dissatisfaction of their customer seems to warrant it, even if they could get away with a warranty claim.
This is the reason that so many of them are not “fans” of memory foam because they know that they are far more likely to have issues of softening and degraded performance which the customer will believe are covered by a warranty when they aren’t. A 10 year warranty on a good memory foam mattress is far more realistic and anything beyond this is really luck of the draw … or a consumer sleeping on foam which has softened significantly and is no longer even close to its original “specs” but which is not yet outside of the warranty exclusions.
Long warranties with warranty exclusions … along with the tendency of polyfoam and memory foam to soften long before it breaks down enough to cause a warranty triggering impression are part of what has allowed major manufacturers to eliminate 2 sided mattresses and put way too much cheap foam in pillowtops and eurotops and “sell” both of them as a “benefit” without having to worry about warranty claims. They are ultimately responsible to their shareholders and ownership not the consumers who use their mattresses so “managed perceptions” in mattress showrooms work in their favor while they work against local manufacturers. Warranties only cover defects and the loss of comfort and support over time or even quickly if a mattress uses lower quality materials is not considered to be a “defect” and is not a warranty issue … even though it may lead to the need to replace the mattress.
Warranties of 20 years or 25 years are all about justifying a higher price and have little to nothing to do with “protection” of the consumer against manufacturing defects (which is the only thing a warranty covers) which will usually show up very early in the life of a mattress. They are used as one of many methods to “step up” a customer into a more expensive mattress using thicker layers of mostly unnecessary and undesirable foam using the belief that if the warranty is longer then the materials or the mattress itself must be better. They have made enormous profits cultivating the belief and the showroom “instant gratification” perceptions that thicker is better.
I would also keep in mind that almost all warranty exchanges have costs involved and these can sometimes be significant. There is often a cost involved in having an inspector come out and check if a mattress meets the warranty criteria and or to have a new mattress delivered. Because the customer is usually responsible for getting the mattress to a drop off point, if there is shipping required then this can involve a substantial cost that is also the responsibility of the customer. This is all a “standard” part of warranties in the industry (and other industries as well). This is also a big reason to make sure you know the quality of the materials inside your mattress (especially in the upper layers … see this article) which can be a much more reliable indicator of the useful life of a mattress than the length of a warranty.
There is also more about all the variables that can affect the durability and useful life of a mattress relative to each person in post #4 here and the posts it links to.
I personally would be happy with a 5 year warranty (against manufacturing defects) if I knew the materials could last me 15 - 20 years … but of course the vast majority of consumers would believe that a mattress with a 5 year warranty was an inferior mattress.
There is also a good beducation video about mattress warranties here.
As to how any density of memory foam will feel to a consumer … the answer is that it really depends on its formulation. “Soft” depends on how it is defined … and before I get accused of hedging the question … let me explain.
The hundreds of different memory foam chemical formulations and manufacturing variations that are possible within the same density of memory foam have different degrees of various properties.
One of these is temperature sensitivity. Memory foam that is more temperature sensitive but also denser will feel firmer when it is colder but softer when it is warmed up. It takes longer to conform to the body shape but when it does so higher density foam will feel “softer” to many people because it can conform to the body better. So it will feel firmer with quicker movements but may feel softer when you have been in a certain position for a while. For someone who moves a lot … they will call it firmer. For someone who tends to be more still … they may call it softer.
Another characteristic is speed of compression and recovery. Memory foam is time dependent. If you compress it quickly … it will feel firmer (like compressing water quickly when you slap it or bellyflop). When you compress it slowly … it will feel softer. Some memory foam will be easier to compress quickly and these are typically the lower density foams. Because of this … people with different weights and sleeping patterns and who tend to compress the foam underneath them either faster or slower will tend to perceive similar memory foams in different ways.
Third … lower density memory foams will tend to also have a lower functional ILD which means that in combination with the thickness of the layer you may feel the layers under them more than higher density memory foams which can also quite dramatically affect the perception of softness of firmness.
Finally … all of these tendencies can be altered with chemistry or mechanical processes so that even in the same density … a memory foam can have an amazingly wide variety of performance specs (see post #9 here). Additions to the foam when it is poured (such as latex infused memory foam or gel infused memory foam) can also make a big difference.
So … with all these variables and more being taken into account … I will say that 4 lb memory foam foam in the way it is usually formulated by most companies will usually feel softer than 5 lb (or 7 or 8 lb) memory foam in most uses. They will also tend to be more “responsive” (compress and come back faster) and less temperature sensitive. In addition to this … they are usually layered in a way (as in the Cloud series) that will increase the perception of softness of a mattress.
Finally on to your question about the lightly used Tempurpedic. I believe that Tempurpedic is a high quality memory foam mattress (although I would also consider that there are many other memory foams that have similar quality/density) and the issues I have with them are more to do with their value compared to other mattresses that use the same or higher quality/density materials and sell at much lower prices. If the price was right and you didn’t have an issue with who had used the mattress before you … then this could very well be your best “memory foam” value since there should be lots of life left in it.
Phoenix