Density & Quality - Direct Correlation?

[phoenix]

Hi sliceoflife,

After reading through much of the materials provided here, I see that the density of the foam as well as the support/base layers seems to be the most important factor in choosing a mattress, and the ILD is usually not too relevant. I’m still confused by a few things:

When you sleep on a mattress the upper layers and components in the mattress will compress and deflect more than the deeper layers or components partly because the comfort 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 layers above them absorbing some of the compression forces first. It’s this constant deflection of the materials in the upper layers of the mattress that softens and breaks down the foam materials and leads to the loss of comfort and support of the mattress over time.

What this means is that the upper layers of a mattress are generally the weakest link of a mattress and will usually have a bigger effect on the durability and useful life of a mattress than the deeper layers in a mattress.

The density of polyfoam and memory foam is the single biggest variable that affects the durability and useful life of the material and density isn’t directly related to firmness. Any specific density of memory foam or polyfoam can be made in a range of firmness levels although firmness/softness is a secondary durability factor as well because softer layers will compress and deflect more and be less durable than firmer layers of the same material.

With latex density is directly related to firmness/softness so a latex layer that is the same type and blend of latex as another layer and is the same density will generally have a similar firmness as well but different types and blends of latex can have different firmness levels for the same density so this only applies to comparing density and firmness with the same type and blend of latex. Durability isn’t an issue with latex because any type or blend of latex would be a durable material relative to other types of foam although they can have different properties and a different “feel”. There is more information about the many variables that can affect durability in the durability guidelines here.

1) When assessing the “quality” of a foam mattress, is there such a thing as “premium” medium density foam and “low-grade” high density foam, i.e. would it be possible for a 3 lb foam be “better” than a 5 lb foam because the “quality” of the former is better? I see some high-priced mattresses with only 3 lb foams, and I can’t help but wonder if their foam is somehow “different” than the cheaper alternatives.

Strictly in terms of durability … the chemical formulation of memory foam and polyfoam can have “some” effect on durability but this isn’t something that I would take into account because density is the single biggest factor and is what I would use when comparing the materials in a mattress to the durability guidelines to identify any lower quality materials or weak links in a mattress. Once again though … the density has little to do with the firmness or “feel” of memory foam or polyfoam because outside of durability there are a wide range of different properties that can be formulated into different foam materials such as firmness, resilience, temperature sensitivity, point elasticity, and compression modulus (the rate that a foam becomes firmer as you sink into it more deeply) with different versions of the same type and density of foam.

In other words … with memory foam and polyfoam density is a “quality/durability spec” and firmness or ILD/IFD is a “comfort spec”. Comfort specs will have more to do with how well you sleep on a mattress and durability specs will have more to do with how long you sleep well on the same mattress.

I recently purchased a cheap memory foam mattress for a guest room, and I weighed the darn thing before opening it up. Based on my calculations, the claim that it has 4 lb memory foam and 1.8 lb base foam seems valid, but it felt way too soft for me. If the firmness of memory foam is fairly consistent with its density, then I know that I will have to definitely purchase higher grade of foam. BUT, again, I see a lot of people complaining about some mattresses being too firm when they’re only 3 lbs…@@

I would always keep in mind that there are no “standard” definitions or consensus of opinions for firmness ratings and different manufacturers can rate their mattresses very differently than others so a mattress that one manufacturer rates as being a specific firmness could be rated very differently by another manufacturer. Different people can also have very different perceptions of firmness and softness compared to others as well and a mattress that feels firm for one person can feel like “medium” for someone else or even “soft” for someone else (or vice versa) depending on their body type, sleeping style, physiology, their frame of reference based on what they are used to, and their individual sensitivity and perceptions. There are also different types of firmness and softness that different people may be sensitive to that can affect how they “rate” a mattress as well (see post #15 here) so different people can also have very different opinions on how two mattresses compare in terms of firmness and some people may rate one mattress as being firmer than another and someone else may rate them the other way around. This is all relative and very subjective and is as much an art as a science.

You can assess a mattress for durability based on the type and quality of the materials and components inside it but the only way to know for certain how a mattress will “feel” to you in terms of comfort, firmness, and PPP (Posture and alignment, Pressure relief, and your own Personal preferences) and how well you will sleep on it will be based on your own careful testing (hopefully using the testing guidelines in the tutorial) or your own personal experience when you sleep on it regardless of anyone else’s experience on the same mattress.

Phoenix