Updated: Jan 31, 2020
How Is Foam Density Measured?
When shopping for foam-based mattresses, you will likely come across density specifications for some models. Density, a weight measurement, can be used to indicate how firm a mattress will feel to sleepers; it is calculated by determining the mass of a one-cubic-foot section of the mattress, and expressed in pounds per cubic foot (PCF). This page will discuss how foam density affects firmness, durability, price, and other mattress factors.
How Is Density Measured?
The term density refers to an object’s mass or weight per unit of volume; to calculate density, simply divide an object’s mass or weight by the total number of volume units. Density measurements are expressed in the following way: [units of weight] per cubic [unit of volume].
When it comes to mattress foam, density is almost always expressed in pounds per cubic foot (or PCF). Let’s say a unit of mattress foam has a density of five pounds per cubic foot; this simply means that each cubic foot of the foam weighs five pounds. If you multiply the density by the total number of volume units, you can calculate the overall weight of the mattress.
How Is Foam Density Categorized
Generally speaking, mattress foam density is divided into three categories:
Low-density foams are relatively soft, and instantly react to a sleeper’s body with shorter break-in periods. They also tend to deteriorate faster; as a result, mattresses with low-density foams usually have below-average price-points.
Medium-density foams, as the name suggests, offer a balance of softness and firmness; they react faster than high-density foams, but not as fast as low-density foams. These foams also fall between low- and high-density foams in terms of durability and price-point, as well as other performance metrics.
High-density foams are relatively firm, and do not react as quickly as low- or medium-density foams; the break-in period is relatively long as a result. These foams also have above-average lifespans, and are typically found in more expensive mattress models.
Density is also linked to ‘temperature sensitivity’, which refers to the way foam conforms to a sleeper’s body when it is warm or cold. High-density foam is considered the most temperature sensitive because it conforms very closely when it is warm, and offers little to no conforming when it is cold. Low-density foam, on the other hand, is less sensitive to temperature changes; its conforming abilities will not significantly change whether it is warm or cold.
The terms ‘low-density’, ‘medium-density’ and ‘high-density’ are associated with specific density measurement ranges. However, it’s important to note that the measurement ranges vary by foam material. The table below lists the density measurement ranges for the two most popular mattress foam materials, conventional polyfoam and memory foam.
What is the Difference between Density and Indentation Load Deflection (ILD)?
In addition to foam density, many mattress manufacturers list the indentation load deflection, or ILD, of foams used in their products. ILD indicates how much pressure is required to make an indentation in a mattress foam layer, and can be used to evaluate firmness; the higher the ILD, the firmer the mattress. ILD measurements for polyfoam mattresses typically range from 24 to 45, while the ILD for memory foam mattresses ranges from 10 to 20.
Density and ILD are often used interchangeably, but it is important to distinguish between these two measurements: density calculates mass per volume unit, whereas ILD only indicates how firm or soft the foam is. ILD has no bearing on foam density; a low-density foam could have a high ILD, or vice versa.
How Does Foam Density Affect a Mattress?
Density can impact mattresses in many ways. The following table compares low-, medium-, and high-density foams based on price, durability, heat retention, and other performance factors. All ratings and figures have been generated using authentic customer experiences with foam-based mattress brands.
Which Foam Density Is Best for You?
Your body weight can help determine which mattress density is best for you. Generally, those who weigh 130 pounds or less tend to feel most comfortable on low-density foams; medium- and high-density foams do not conform as closely under sleepers with below-average weights, and the result is often more back pressure. Likewise, heavyweight sleepers tend to sink further on high-density foams, which can cause discomfort.
The table below compares foam density types based on three different weight classes.
Ease of movement is another factor. Because high-density is so sensitive to temperature changes, the material conforms more closely to sleeper’s bodies. This can be beneficial to those with back pain or pressure, but others complain of a ‘sinking feeling’ when the foam is too warm and difficulty getting off the mattress. Low-density foam, on the other hand, is easier to get on or off, but it will not conform as closely (or alleviate as much pressure) as most medium- or high-density foams.
In order to find the right mattress for them, shoppers are encouraged to understand the role density plays in a foam mattress and research the density specifications of different models. Most mattress manufacturers list foam density in their product specifications. Shoppers should reach out to customer service representatives if this information is not available.