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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 at least 6,930 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 more detailed analysis.
(2 - 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-|
|Easy to move on||b-||c||d|
|Back sleep friendly||b||b+||a-|
|side sleep friendly||b+||b||b-|
|front sleep friendly||b||c+||c-|
|Good for sex||c+||c||c-|
* 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, the mattresses often have fairly different strengths, weaknesses and characteristics depending on their density.
The price of a memory foam mattress is often linked significantly to its density. The more dense the memory foam, 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 nine years. This is only an average, however; the longevity of a particular mattress can vary from the average 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 from the average 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. 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 and minimization of pressure points.
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 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 a supportive and firm regular foam base. This limited use of memory foam can result in the bed feeling excessively firm.
High-density memory foam beds, by contrast, tend to use a generous amount of memory foam which increases 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, but often only 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 can also mean that turning over or changing positions on a high-density mattress can mean that the new area of the bed the sleeper has moved to will be firm until body heat warms it.
Medium-density mattresses, like high-density mattresses, tend to use a substantial amount of memory foam resulting in less firmness. However, medium-density foam is less temperature sensitive than high-density foam. As a result, medium-density beds have fewer complaints about being excessively firm when cold.
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 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-gel-infused memory foam.
Higher density memory foam is often 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 strong contouring-to-the-body feeling.
Most owners of higher-density mattresses like the temperature sensitivity or at least learn to appreciate it. Some, however, do not like it and say it causes the mattress to be too firm when getting into bed, but then as the bed warms it feels like one is sleeping in "mud" or "quicksand."
Less-dense foam mattresses, by contrast, are less temperature sensitive and consequently feel more like a conventional bed.
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 weaker, 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 more dense the memory foam is, the more it will weigh. 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-density memory foam beds almost always have at least a 20-year warranty, and usually the first 10-15 years are non-prorated. Medium-density mattresses usually have a 10-20 year warranty with half of this time being non-prorated. Low-density beds have a wide variety of warranty lengths, but most are 5-10 years in length, often with the entire length being non-prorated.
Our comparison findings are based on the experiences of 6,940 actual memory foam mattress owners.
The mattress owner experience data was collected from diverse and credible sources.
– Memory foam mattresses with low and medium density on average have a shorter lifespan (typically 4-8 years) than high density beds (at least 6 years on average).
– 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.
– 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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