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Density, or weight per unit of volume, is an important variable for mattresses with foam components. Foam density also affects other factors associated with the mattress, such as durability, motion isolation, odor potential, and cost.
This guide will discuss how density is measured for polyfoam and memory foam mattress layers, and provide buying tips for selecting beds based on density measurements.
Density refers to how much one cubic foot of foam weighs; it is expressed in pounds per cubic foot (PCF). To calculate density, divide the mass or weight of an object by the total number of volume units. For example, a foam layer that weighs 100 pounds and measures 25 cubic feet has a density of 4 PCF; assuming the foam has a uniform consistency, every square foot of the layer will measure 4 pounds.
Two types of foam are widely used in mattresses made today. Flexible polyurethane foam, also known as polyfoam, is a synthetic material produced from polyol and isocyanate petrochemicals. The other foam type is viscoelastic polyurethane foam, or memory foam, a specialized polyfoam engineered to become softer when it comes into contact with body heat and then return to its original shape when cooled. Polyfoam is relatively inexpensive, and widely used in the support core, or base layers, of mattresses; select models also feature polyfoam in the topmost cushioning layers, known as the comfort layers, or transitional layers between the comfort and support layers. Memory foam, on the other hand, is too soft and not dense enough to serve as a support core material; it is almost exclusively used as comfort or transitional layers.
Additionally, foam density falls into three general categories: low, medium, and high. High-density foam is almost always used in mattress support cores, and may also be used as a comfort or transitional layer. Low- and medium-density foams are only found in the bed’s comfort system; if used as a support core material, these foams would lead to excessive sagging and uneven sleeper support.
Density is used to evaluate both polyfoam and memory foam, but the PCF ranges differ considerably. The table below breaks down PCF ranges for low-, medium-, and high-density polyfoams and memory foams.
|Material||Low-Density Range||Medium-Density Range||High-Density Range|
|Polyfoam||Less than 1.5 PCF||1.5 PCF to 1.7 PCF||More than 1.7 PCF|
|Memory foam||Less than 4 PCF||4 PCF to 5 PCF||More than 5 PCF|
Some mattress brands use the terms ‘density’ and ‘firmness’ interchangeably, but this is technically incorrect. While density is a weight/volume measurement for individual mattress layers, firmness refers to how soft or firm the whole mattress feels, and how closely the comfort layer material conforms to the sleeper’s body. Firmness is measured on a 1-10 scale, with 1 being softest and 10 being firmest; most mattresses sold today fall between 3 and 8.
The firmness of individual foam layers may also be measured in indentation load deflection, or ILD. ILD is calculated by placing a circular disk measuring 1 foot in diameter on a section of foam that measures about 4 inches thick. The ILD is the amount of weight needed to compress that section of foam by 25%; ILD is expressed in numerals corresponding to the weight. The foams used in mattress comfort layers usually fall between 10 and 20; transitional layer and support core foams usually have much higher ILD measurements.
Although density and firmness are technically different measurements, there is some overlap. High-density foams tend to be firmer and do not conform very closely, while low- and medium-density foams are not as firm and conform more.
The density of foam layers used in a mattress can impact many different aspects of the overall bed. The table below breaks down how low-, medium-, and high-density foams affect some these variables. Our ratings are based on a combination of verified owner experiences and product research and analysis.
|Durability||Poor Low-density foam is more susceptible to sagging and early wear-and-tear, giving mattresses with this material a shorter-than-average lifespan||Fair to Good Medium-density foams are more durable than low-density foams, but some sagging and early wear-and-tear may still occur||Good to Very Good High-density foam has strong longevity; beds made with this material typically have longer-than-average lifespans|
|Conforming ability||Poor to Fair Low-density foams do not respond to the sleeper’s body temperature as much as higher-density foams, resulting in a minimal amount of body conforming||Good to Very Good Medium-density foams conform fairly consistently, though they don’t provide the same close body hug as high-density foams||Very Good High-density foam conforms closely and consistently to the sleeper’s body, due in part to its high responsiveness to body heat|
|Pain/pressure relief||Fair to Good Because low density foams tend to conform very little, sleepers may not experience as much pain and pressure relief; that being said, most foam mattresses alleviate discomfort to at least a noticeable extent||Good Most mattresses with medium-density foams – especially memory foam – provide decent pain and pressure relief for sleepers||Very Good High-density foams earn strong ratings for pain and pressure relief due in part to their close conforming ability|
|Temperature neutrality||Good Low-density foams do not absorb and trap as much body heat, allowing them to sleep cooler than denser foams – but temperature neutrality is still average at best||Fair to Good Medium-density foams trap a fair amount of body heat from sleepers, and will likely be too warm for some people||Poor to Fair High-density foams can be major heat traps, and are not recommended for those who tend to sleep warm or hot|
|Sex||Fair to Good Foams are generally considered worse for sex than other mattress materials because of their low responsiveness, but low-density foams are springier and may be suitable for some couples||Poor to Fair Medium-density foams are not very responsive; as a result, some couples claim that having sex on these materials results in a sinking feeling they liken to fighting with the mattress||Poor High-density foams are temperature-sensitive and often sink excessively; as a result, many couples complain beds with these foams are not good for sex|
|Motion isolation||Good Motion isolation is a strength of all foams, but low-density foams tend to minimize the lowest amounts of transfer||Very Good Most medium-density foams absorb and minimize a significant amount of motion transfer||Very Good Like their medium-density counterparts, high-density foams offer strong motion isolation|
|Noise potential||Excellent With rare exception, mattresses with low-density foam are virtually silent when bearing weight||Excellent Medium-density foam does not make any noise when bearing weight||Excellent Noise potential is an area where all foams excel regardless of density; high-density foams are virtually noise-free as well|
|Odor potential||Fair Most mattresses with foam components produce off-gassing odor when new, but those with low-density foams tend to produce the lightest and least persistent smells||Fair to Poor The denser the foam, the higher the odor potential; most medium-density foams emit stronger and longer-lasting smells than low-density foams||Poor The strongest and most persistent off-gassing odors are associated with mattresses containing high-density foam layers in the comfort system and support core|
|Mattress weight||Low Mattresses with low-density foam tend to be lightest; the average weight is about 50 to 65 pounds||Moderate Medium-density foam can drive up the weight by a noticeable degree; the average mattress weight is about 60 to 75 pounds||High High-density foam is naturally the heaviest; beds with high-density foam comfort layers and support cores typically weigh 75 to 90 pounds, or more in some cases|
|Average price||Low Because low-density foam is relatively inexpensive, mattresses with this material have the lowest average price-point: about $500 to $750||Moderate Mattresses with medium-density foams have middle-of-the-road price-points: about $700 to $950 on average||High Expect higher-than-average prices for mattresses with high-density foam layers outside the support core: about $1,000 to $1,400|
When selecting a mattress based on the density of its foam layers, shoppers should take their weight into account. Lighter people tend to prefer lower-density foams because they do not experience as much conforming/pressure relief on higher-density materials. The opposite is true of heavier people; sleeping on lower-density foams often leads to excessive sagging and less-than-optimal support.
Preferred sleep position is another important factor. Side sleepers usually need a softer, lower-density mattress that will cushion their shoulders and hips; this improves spinal alignment and alleviates aches and pains. Back and stomach sleepers utilize positions that naturally align the spine, but excessively soft mattresses can sink beneath the heavier areas of their body; this causes the sleep surface to become uneven, and can cause more pressure points to develop.
The table below lists average ratings for different foam densities based on these two criteria.
|Sleep Position||Ideal Density for Lightweight Sleepers (Less than 130 lbs.)||Ideal Density for Average Weight Sleepers (130 to 230 lbs.)||Ideal Density for Heavyweight Sleepers (More than 230 lbs.)|
|Side||Low to Medium||Medium||Medium to High|
|Back||Low to Medium||Medium to High||High|
|Stomach||Medium||Medium to High||High|
Now that we’ve discussed what foam density means and how it is used in mattress construction, let’s look at the density measurements for mattresses sold today. The table below includes comfort layer and support core density figures for some of the today’s most popular all-foam beds, along firmness levels and current price-points.
To read our reviews of these brands, please click the links found in the left-hand column; to view product pages, click the links in the second column from the left.
|Mattress Brand||All-Foam Model||Comfort Layer Composition||Support Core Composition||Firmness Options||Price (Queen)|
|Bear||Bear Mattress||1" memory foam (4 PCF) 2.5" polyfoam (3 PCF)||6.5" polyfoam (1.8 PCF)||Medium Firm (6.5)||$840|
|Casper||The Casper Mattress||1.5" memory foam (4 PCF) 1.5" polyfoam (2.5 PCF)||5" polyfoam (1.8 PCF)||Medium (5.5)||$896|
|Ghostbed||Ghostbed||1.5" synthetic Dunlop latex 2" 2" memory foam (4 PCF)||7.5" polyfoam (1.8 PCF)||Medium Firm (6)||$895|
|Layla||Layla Mattress (flippable)||Side 1: 3" memory foam (3.5 PCF) 2" polyfoam (1.8 PCF) Side 2: 1" memory foam (3.5 PCF)||4.5" polyfoam (2 PCF)||Side 1: Medium Soft (4) Side 2: Firm (7)||$874|
|Leesa||Leesa Mattress||2" polyfoam (3 PCF) 2" memory foam (3 PCF)||6" polyfoam (1.8 PCF)||Medium (5)||$795|
|Nectar Sleep||Nectar Mattress||1" memory foam (4 PCF) 3" memory foam (3.5 PCF)||7" polyfoam (2.2 PCF)||Medium Firm (6.5)||$699|
|Novosbed||Novosbed||2" memory foam (3.7 to 5 PCF) 2" memory foam (4 to 5 PCF)||6-7" polyfoam (1.8 PCF)||Soft (3.5) Medium (5) Medium Firm (6.5)||$999|
|Puffy||Puffy Mattress||2" memory foam (2.5 PCF) 2" polyfoam (density not disclosed)||6" polyfoam (1.5 PCF)||Medium (5)||$850|
|Saatva||Loom & Leaf||2.5" memory foam (5 PCF) 2" memory foam (4 PCF)||2" polyfoam (1.6 PCF) 5.5" polyfoam (1.8 PCF)||Medium (5.5) Firm (8)||$1,499|
|Tuft & Needle||T&N Mattress||3" polyfoam (2.8 PCF)||7" polyfoam (1.8 PCF)||Medium Firm (6.5)||$595|