Conversely, mattresses with very high-density support cores can still feel soft overall. Put another way, density is the ratio between mass and volume or mass per unit volume. Such techniques include the use of a hydrometer (a buoyancy method for liquids), Hydrostatic balance (a buoyancy method for liquids and solids), immersed body method (a buoyancy method for liquids), pycnometer (liquids and solids), air comparison pycnometer (solids), oscillating densitometer (liquids), as well as pour and tap (solids). bulk density, skeletal density, etc. Density is calculated by the dividing the mass by the volume, so that density is measured as units of mass/volume, often g/mL. Density is commonly expressed in units of grams per cubic centimetre. In summary, density is a measure of individual components of a mattress. In the case of foam, it is measured in pounds per cubic foot (PCF). Commonly used foams include polyfoam, latex, and memory foam. You may see 2-4 separate layers of different foam materials in a single mattress, each of which may have a substantially different density rating. Density is essentially a measurement of how tightly matter is crammed together. Density has a significant influence on how the foam feels and performs. A mattress may be topped with a relatively low-density foam comfort layer, but still feel like a firm mattress overall. For example, the density of water is 1 gram per cubic centimetre, and Earth’s density is 5.51 grams per cubic centimetre. In summary, density is a measure of individual components of a mattress. Firmness is a measure of the entire mattress. Within each category of foam, one may find dozens of variations in density and firmness. Temperature Neutrality Each distinct layer, including various foam comfort layers, support cores, and even metal springs where relevant, all contribute to how a mattress feels. "National Sleep Foundation" and the other marks listed on this website are federally-registered trademarks of the National Sleep Foundation and are used here with permission from the National Sleep Foundation. They offer better airflow, and do not absorb as much body heat, compared to high-density foam materials. When comparison shopping, be sure to double check the type(s) of foam, and not just the density rating. As you can see from the table, the range that is considered “high density” for polyfoam is much different than the same range for memory foam. They are less susceptible to sagging, and also more resistant to accidental damage and tears. Price Denser foams are typically more durable than low-density foams, and will not sag as much over time. This disconnect can also make it somewhat confusing to compare foam densities on multiple mattresses. The units of density depend on the units used for mass and volume, but are usually: g/cm³ (if mass is measured in g and volume in cm³). A bed utilizing primarily low-density foam will typically weigh between 50 and 60 pounds, while a high-density foam mattress may weigh 90 pounds or more. Higher-density foams generally conform closer than low-density foams and thus offer better pressure relief than lower-density foams. Because of these properties, manufacturers often use a mix of foams with various density ratings. This produces that quality that memory foam is known for, where an impression from your body or object lasts in the foam for a few seconds. A material's density is defined as its mass per unit volume. We’ve covered how foam density is measured, and how to calculate it – but what does it actually mean? On the other hand, low-density foams tend to offer better temperature regulation, which can be an important factor for those living in warm climates. Low-density foams weigh much less than high-density materials. For these reasons, low- to medium-density foams tend to perform best for sex. As an example, consider a foam layer that weighs 100 pounds and measures 25 cubic feet in total. The section below goes over some other factors to consider. By dividing the total weight by the total number of cubic feet (100 divided by 25, in this case), we can see that this layer has a density of 4 pounds per cubic foot (4 PCF). Density is simply a measurement of weight per unit of volume. A table covering the various density ranges for foams can be found below. The formula for density is d = M/V, where d is density, M is mass, and V is volume. Denser foams are more durable and tend to outlast lower-density materials. This is due to the different properties of each material. How Foam Density Affects Mattress Performance. Mattress support cores typically utilize high-density polyfoam or latex, while comfort layers utilize foams of a variety of densities. Because foam density is such a significant factor in the performance and feel of each mattress, it’s a good idea for mattress shoppers to understand foam density measurements. SleepFoundation.org does not provide medical advice, diagnosis, or treatment options.