Memory Foam Mattress Density Guide

When you’re shopping for the best mattress, you’re likely to encounter the term “density” as it relates to memory foam. Density can be a difficult concept, but once you understand it, density can tell you a lot about a mattress’s likely comfort and durability.

In this buying guide, we discuss what density is and what memory foam is, along with the different foam densities on the market. We also explain the difference between density and firmness and answer a few frequently asked questions.

What is Density?

Density is the measure of mass in a given volume to determine how close together or far apart particles are. The denser a material is, the more it weighs per a given amount.

When we discuss memory foam density, we do so using units of cubic feet. Heavier foams have a higher density per cubic foot.

What is Memory Foam?

Also known as viscoelastic foam, memory foam is polyurethane foam modified to respond to heat and pressure. So when you lie down on top of a memory foam mattress, the bed molds itself around your body weight and warmth. Once you stand up, the bed snaps back to its original shape.

Many owners enjoy sleeping on a memory foam mattress for the pressure relief and motion isolation it offers. As memory foam contours close to your body, it leaves no part unsupported and prevents pressure from building up. Memory foam’s malleability allows it to absorb movement, which prevents you from disturbing a partner’s rest or vice versa.

Memory foam has two big drawbacks. One is an issue with retaining body heat, which may wake you in the night if your mattress grows too hot. Many manufacturers add conductive materials to the foam such as gels, charcoal, and copper, or they substitute certain petrochemicals with plant-based chemicals to create a cooling mattress.

New mattresses may have an odor in the first week, as volatile organic compounds (VOCs) from the production break down upon exposure. The process of VOCs breaking down is known as off-gassing, and most mattresses lose the smell after three to seven days.

A foam’s density can affect how much pressure relief it offers, how well it prevents motion transfer, how much heat it retains, and how long it spends off-gassing.

The Different Densities

There are three foam densities—low, medium, and high density. By looking at a foam’s density, you can judge its probable cost, durability, and comfort level.

Low-Density

Low-density foam weighs 3 pounds or less per cubic foot. Low-density foams are inexpensive as they contain relatively little material, which also helps them to retain less body heat than other densities. However, since they contain so little material, low-density foams often wear out within 6 years and may not provide as much pressure point relief as other densities.

As low-density foams have short lifespans, they’re not the best choice of mattress to sleep on night after night unless you’re shopping on a tight budget. However, they’re excellent choices for a guest bedroom. Low-density mattresses are also a good choice for children’s beds, as children place less pressure on a bed than an adult, extending the mattress’s lifespan.

Medium-Density

Medium-density foam weighs 4 to 5 pounds per cubic foot. Medium-density foam is an excellent middle-of-the-road option—it’s not too expensive, doesn’t retain too much heat, and molds itself close to the body for pressure and pain relief. These foams tend to have decent durability, lasting around 7 years or so.

High-Density

High-density foam weighs 6 or more pounds per cubic foot. Of the three, high-density memory foam provides the best back pain relief and motion isolation. Many owners find it’s the most comfortable option because it conforms closely to the body. High-density foam is also the most durable option, likely to last at least eight years–this is why it’s often used as the support layer, although you can find mattresses with high-density foams in its comfort layer.

Since high-density foam contains more material, however, they are the most expensive and may need more time to off-gas. Some owners also report long break-in periods and that high-density foams conform too well to their bodies, leaving them feeling stuck in the mattress.

Firmness and ILD

While many customers conflate a memory foam mattress’s density with its firmness, the two are not the same. A higher density foam doesn’t necessarily mean a firmer mattress.

Instead, most companies measure a mattress’s firmness using its Indentation Load Deflection (ILD) rating. An ILD rating is a measure of how much force it takes to compress a material to 25 percent of its thickness. The higher the ILD number, the firmer the material is.

The ILD rating is a bit technical, which is why not every company openly advertises it. If you’re interested, you may have to reach out to customer service.

Many companies simplify firmness ratings with a 1-10 scale, with 1 as the softest option and 10 as the firmest. This number is translated into a label such as “firm” or “medium-soft.” These labels are an easier way to get an idea of how a mattress feels.

Firmness RatingFirmness Description
1Extra-soft
2 and 3Soft
4Medium-soft
5Medium
6Medium-firm
7 and 8Firm
9 and 10Extra-firm

Other Types of Mattress Foams

Memory foam isn’t the only type of foam bed on the market. You may want to consider alternatives such as latex foam and polyurethane foam.

Latex foam comes in two types, natural and synthetic. Manufacturers produce natural latex from rubber tree sap for an environmentally friendly material, while synthetic latex is made from chemical compounds. Of the two, natural latex is the more durable option.

Polyurethane foam is a low-cost substitute for memory foam. It has low-density and a shorter expected lifespan than memory foam, but it still conforms to your body to relieve pressure.

Frequently Asked Questions

What is the best firmness for a memory foam bed?

There is no one best firmness, as the firmness right for you depends on your sleeping position, body type, and personal preferences. A memory foam mattress for side sleeping should have a soft to medium feel, while back sleepers and stomach sleepers need a medium-firm to firm mattress.

Petite sleepers need a softer than usual mattress, while the best mattress for a heavy sleeper is on the firmer side.

What is meant by high-density foam?

High-density means that the foam’s materials are concentrated, with more particles packed into a cubic foot than in a lower density foam. This typically gives high-density foam greater durability than lower density foams.

Is high-density foam firm or soft?

It’s a common misconception that high-density foam feels firm because soft high-density foams exist, too. Density is a mark of a material’s durability rather than its firmness level.

Did We Help?

The best foam density for you will offer a comfortable night’s sleep while fitting within your budget restrictions. Remember that density is not the same as firmness, as a high-density foam can feel firm or soft depending on its manufacturing process. Reading through customer reviews and buying a mattress with a lengthy sleep trial will help you find the mattress right for you.

This article is for informational purposes and should not replace advice from your doctor or other medical professional.

Michelle Zhang, Wellness Writer Michelle Zhang

Michelle Zhang is a regular contributor to our Zoma blog and is our go-to sleep researcher. In her time with Zoma, Michelle has researched and published many articles on widespread sleeping habits and troubles. In her time outside of Zoma, Michelle is an occupational therapist and long-distance runner. She believes leading a healthy lifestyle is the key to getting better sleep at night.

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