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The density of memory foam often determines many mattress characteristics as well as many differences between brands / models. You can often learn much about a memory foam mattress simply by knowing its density. (To learn the density of many popular memory foam mattresses, see the memory foam mattress ratings – summary.)
In most areas of comparison, low- and medium-density memory foam mattresses tend to perform as well as and often better than high-density memory foam mattresses.
Density indicates how much the foam weighs. For example, a cubic foot of four lbs/ft density foam weighs four pounds.
The findings below are based on a sample size of 6,900+ actual memory foam mattress owners. The findings are true for memory foam mattresses as a group; individual brands / models and individual owner experiences may go against these findings somewhat. Refer to the comparisons below this table for detailed analysis.
(2.5 - 3 lbs/ft)
(5 lbs/ft +)
|Durability / longevity||c+||b-||b|
|Less (Back) pain||b-||b||b+|
|No initial odor||c-||d+||d+|
|No sleeping hot||c||c-||d|
|Not overly firm*||c+||b+||b-|
|Not firm when cold||C-||D+||D-|
|Easy to move on||b-||c||d|
|Floating, Cloud feel||B-||B+||A|
|Suited for all Positions||b||b+||C|
|Short break in||B-||C-||d|
|Easy to lift, transport||c+||c-||d|
|Good for sex||c+||c||D+|
* Memory foam firmness is measured by IFD (indention force deflection), not by density. Nevertheless, memory foam mattresses of particular densities tend to fall under certain firmness categories as the ratings above and further analysis indicate.
Memory foam mattresses, regardless of their density (low, medium or high), have about the same owner satisfaction rate – around 80%. Nevertheless, mattresses of different density often have fairly different strengths, weaknesses and characteristics.
The price of a memory foam mattress often depends to an extent on its density. All other things being equal, the more dense the memory foam is the more expensive the mattress usually is.
Higher-priced brands will tend to use higher-density memory foam (5 lbs/ft or greater in significant quantity); medium-priced brands will tend to use mostly medium density (4.0 lbs./ft); and lower-priced brands will tend to use mostly lower density (2.5 - 3.0 lbs./ft).
On average, the higher the memory foam density is, the better the durability / longevity of the mattress. Mattresses with high-density foam can generally be expected on average to remain supportive and comfortable for around 8.5 years. This is only an average, however; the longevity of a particular mattress can vary considerably.
Memory foam mattresses with low and medium density tend to have a shorter lifespan, often in the 4-8 year range. Again, this is only an average, and the longevity of a particular mattress can vary significantly.
All memory foam mattresses, regardless of density, rate well in regard to pain relief, including relief of back, shoulder and hip pain.
However, higher-density foam often provides better pain relief in most cases, especially back pain relief. This is because higher-density foam tends to strongly conform to the contours of a person's body which can result in excellent support, including optimal spinal alignment.
Owner experience data suggests that, generally speaking, the more dense a memory foam mattress is the longer and / or more strongly it will give off an initial chemical-like odor or gas. More information: memory foam mattress off gassing.
A mattress with good motion isolation absorbs the movement of one person so that it does not transfer across the bed to disturb the other person.
In other words, a mattress with good motion isolation tends to be friendly for couples. All memory foam densities perform well on this issue, but higher density foam isolates movement almost entirely.
"Sleeping hot" is a somewhat common complaint for memory foam mattresses. Most heat trap complaints, however, are for mattresses with medium- and especially high-density foam.
Only about 5% of low-density bed owners report a heat trap problem, while about 8% of medium-density bed owners report a problem. And about 12% of high-density bed owners (especially owners of Tempur-Pedic Contour models Rhapsody, Allura, Grand) report a problem.
Memory foam of any density that is infused with tiny gel beads tends to have fewer heat-related complaints than non-infused memory foam (of similar density) assuming that at least two inches of the material is present.
A conforming mattress is one that strongly molds and contours to a person's body. Higher-density memory foam is often the most conforming because it is the most temperature sensitive. "Temperature sensitive" means that the mattress is firmer in lower temperatures and softer in higher temperatures or when in contact with a person's body heat.
A person tends to sink into or "melt" into a higher density mattress because the foam under the person's body becomes softer but the surrounding foam stays firmer. This can result in good supportiveness and a highly conforming or contouring-to-the-body feeling.
Most owners of higher-density mattresses appreciate the temperature sensitivity or at least learn to. About 15% of owners, however, do not like it and say that the sinking-in effect causes them to feel like they are sleeping in "mud" or "quicksand."
Less-dense foam mattresses, by contrast, are less temperature sensitive and conforming and consequently feel more conventional.
A fairly common complaint among memory foam mattress owners is that their mattress is too firm. Excessive firmness tends, however, to be a problem mainly for low-density mattresses, not high density – as counter-intuitive as this may seem.
The often-reported higher firmness level of low-density mattresses can be explained, in part, by the fact that the beds often use a small amount of memory foam, usually three inches or less, over six inches or more of firm regular foam. This high proportion of firm regular foam often makes the mattress firm overall.
High-density memory foam beds, by contrast, tend to use a generous amount of memory foam and a smaller proportion of firm regular foam. This increases overall mattress softness somewhat. In addition, the superior conforming ability of high-density foam tends to result in minimal pressure points, and this can result in a softer, "sleeping on a cloud" feeling.
High-density mattresses, however, can feel excessively firm when they are cold because of their temperature sensitivity. The foam becomes softer once warm room temperature or the sleeper's body heat warms the foam. Temperature sensitivity also means that when turning over or changing positions to a new area of the mattress, the foam will need time to warm and become softer.
Medium-density mattresses, like high-density mattresses, tend to use a substantial amount of memory foam resulting in less excessive firmness. Medium-density foam, however, is less temperature sensitive than high-density foam. As a result, medium-density beds have fewer complaints about being excessively firm when cold.
Owners of high-density memory foam mattresses usually report that they sink into the foam significantly and that it contours strongly to their body. (See the temperature sensitivity comparison above for why this is so.)
While this can provide good supportiveness and pain relief, it also can result in the mattress being at least somewhat difficult to move on and get up off. Consequently, people who are physically weak, such as the elderly or the sick and disabled, may want to avoid higher-density foam.
Less dense memory foam, by contrast, tends to have more conventional characteristics and is easier to move on and get up off.
The higher the density of foam, the more of a floating and cloud-like sensation a person tends to experience when lying on the mattress. This is due to the fact that the foam tends to envelop and contour strongly to a person's body resulting in equal weight distribution.
Back sleepers tend to be satisfied with any density, but higher-density foam may provide the most support and pain-relief potential.
Side sleepers tend to be most satisfied with medium-density memory foam mattresses.
Some front or stomach sleepers find that they sink too far into high-density foam which may result in poor neck alignment and even breathing difficulty.
High-density memory foam beds tend to require the most break-in time. In other words, they often require the most use before they reach the level of firmness and support that they will provide for the long term.
The more dense the memory foam is, the more it will weigh. Virtually all memory foam mattresses, however, regardless of density, are heavy enough to make moving them, transporting them, and changing their linens at least fairly difficult, especially for one person. High-density foam beds are especially difficult in this way.
The properties of memory foam, regardless of density, can provide certain pros and cons in regard to love making. Owner experience data suggests that lower density memory foam tends to be more suitable overall for love making than higher density foam, namely because lower density foam is easier to move on and has less of a "sinking in" feeling. See the sex and mattresses comparison for more information.
High- and medium-density memory foam beds tend to have 10-20 year warranties with 10 years (or more) being non-prorated. Low-density beds have a wide variety of warranty lengths, but most are 5-10 years in length, with half or all of the length being non-prorated.
The comparison findings are based on the experiences of 6,900+ actual memory foam mattress owners.
The mattress owner experience data was collected from diverse and credible sources.
– Memory foam mattresses, regardless of density, typically have similar owner satisfaction rates, about 80 percent. Nevertheless, memory foam mattresses of different density often have different strengths, weaknesses and characteristics.
– Memory foam mattresses with low and medium density on average have a shorter lifespan (typically 4-8 years) than high density beds (at least 7 years on average).
– Most heat trap or sleeping hot complaints are for memory foam beds with medium- to high-density foam.
– High-density memory foam is often at least somewhat difficult to move on and get up off, while lower-density foam tends to not have a significant problem in this area.
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