Eachnight may earn commissions for products you purchase through our links. Our articles and reviews include affiliate links and advertisements, including amerisleep advertising. Learn more Updated October 11, 2021There are multiple factors to consider when you’re shopping for the best memory foam mattress. How long can I expect the bed to have that new mattress smell while it’s off-gassing? How long should the bed to last? Will the mattress stay cool at night?Much of what you look for in a memory foam mattress is affected by the foam’s density. Knowing a foam’s density can help you determine how durable it is, how quickly it will snap back into shape, how much pressure relief it’s likely to provide, and how much it weighs.What is Density?The dictionary definition of density is that it’s an expression of a material’s mass per unit volume. What this means is that density determines how compact a substance’s particles are. When the particles are close together, they create high density, while a low-density material’s particles are farther apart.Mattress companies measure memory foam density in cubic feet. Manufacturers take a foam block that’s 12 inches on each side and weigh it.Why is Density Important?Mattress density affects several other mattress traits:Price: A high-density foam contains more material, which drives up the mattress’s price.Durability: Low-density mattresses have less material, making them more likely to break down.Contouring: All memory foam mattresses mold themselves to you because of your body heat and weight. However, high-density foams conform more to the body.Weight: The more particles a material has, the more it weighs.Responsiveness: Lower density foams regain their original shape faster. This is because they have more air inside.The Different DensitiesCompanies categorize memory foam as low, medium, and high density. A foam’s classification is determined by how many pounds it weighs per cubic foot.Low-DensityLow-density memory foam weighs 3 pounds or fewer per cubic foot. They’re quick to respond to your movements because they contain more air. While a responsive foam does make getting up easier, it will not offer as much contouring and pressure point relief as a higher density foam.Low-density foams have the lowest prices but only last about 6 years. If you’re considering a mattress for a guest bedroom, a low-density foam mattress can be a good choice. The infrequent usage will help it last longer.Medium-DensityMedium-density memory foam weighs 4 to 5 pounds per cubic foot. Medium-density foams often offer a good compromise between the benefits of low-density and high-density foam. They’re not as expensive as mattresses made of high-density foam and are quicker to finish off-gassing. They provide more pressure and pain relief than a low-density foam mattress.Medium-density foams last about 7 years.High-DensityHigh-density memory foam weighs 5 or more pounds per cubic foot. Of the three densities, high-density foam provides the best motion isolation, back pain relief, conformability, and durability.However, high-density foam has a few drawbacks. The amount of material it contains means it takes a longer time to break in and off-gas than lower density foams. It’s also more awkward to move a high-density mattress since it weighs so much. And high-density foam has the highest prices of the three.High-density foams last about 8 years.Mattress Firmness and ILDMany people confuse a mattress’s firmness with its density, but the two are not the same thing. A lower density foam does not mean a mattress feels softer, and a higher density foam does not imply a mattress feels firmer. Many companies even use high-density foams to create soft comfort layers.Instead of density, mattress companies measure a mattress’s Indentation Load Deflection (ILD) to determine its firmness. The ILD test measures how much force it takes to compress a mattress to 25 percent of its original thickness. Softer materials have lower ILD numbers.Mattress companies then simplify the mattress’s ILD rating with a label such as “medium-firm” or “extra soft.” If you want to learn an ILD rating, you might have to reach out to customer service.The best firmness level for you depends on your preferred sleep position and body type:The best mattress for side sleepers is soft to medium in firmness.Back sleepers sleep best on a medium-firm to firm mattress.Stomach sleepers need a firm mattress to maintain neutral spine alignment.People who weigh less than 130 pounds should look for a softer mattress.People who weigh more than 230 pounds should look for a firmer mattress.More to Look for in a Memory Foam MattressDensity isn’t all you should look at when you’re shopping for the best memory foam mattress. You also should consider its cooling features and off-gassing period.Cooling FeaturesTraditional memory foam can retain too much body heat. So, many manufacturers take preventive measures to keep the mattress cool. Many add cooling materials such as gel foam, copper, charcoal, green tea extract, and ceramic beads.Some companies replace a portion of the petrochemicals used in foam production with plant-based substitutes. This not only creates a more eco-friendly product, but it also promotes airflow in the memory foam.Off-GassingMost memory foam mattresses have an initial chemical smell. The scent comes from volatile organic compounds (VOCs) during production which break down at room exposure. This process is off-gassing, and the smell usually vanishes within three to seven days.If you’re sensitive to smells, look for a mattress with a CertiPUR-US® certification. CertiPUR-US® is an independent organization that verifies a mattress contains low amounts of VOCs. It’s impossible to make a memory foam mattress completely free of VOCs.Memory Foam AlternativesIf you’re looking for a foam mattress, you can consider more than just memory foam. There’s also latex foam and polyurethane foam.Latex foam is naturally firmer than memory foam but still conforms to the body for pressure relief. There’s natural latex, which is made from rubber tree sap. And there’s synthetic latex, which is made from chemical compounds.Polyurethane foam is an inexpensive material made from petrochemicals. It’s often considered a less durable material than memory foam because of its lower prices, although quality poly-foam mattresses can last quite a few years.Other Things to ConsiderHow is memory foam density measured?Density is measured by dividing the foam’s weight by its length, width, and height. This is how density expresses a foam’s weight per cubic foot.What is high-density foam?High-density foam means the particles that make up the foam are compact, so there are more particles per cubic foot. The more particles per cubic foot, the longer it may take for the foam to show wear and tear.How can you tell the quality of foam?A mattress’s warranty can also give you an idea of foam quality. The standard warranty length is 10 years, but many companies that use high-quality foams offer longer warranties. If the mattress warranty is shorter than 10 years, the mattress may contain low-quality foam.What density memory foam topper is best?When looking at mattress toppers, you should find one that includes 4 or 5-pound density foams. These foams are durable and contouring, so they can offer better sleep for years.Is high-density foam firmer?Density and firmness are not one-in-the-same. You can have a super soft high-density layer and an ultra-firm low-density layer. ILD is what plays into firmness. High-density foams are heavier and more durable than low-density foams, though. With that, they’re also less breathable.ConclusionEvery foam density has its advantages and disadvantages. The best memory foam density will offer you a good’s night sleep by relieving pressure and preventing heat from building up.When you’re shopping, keep in mind density and firmness are not the same. To find the right firmness for you, you will need to consider your favorite sleeping position and your body type.About the author Andrea Strand CERTIFIED SLEEP COACH Andrea Strand is a Certified Sleep Science Coach. She earned her Bachelor of Arts degree from Brigham Young University-Idaho where she studied English with an emphasis in Technical Writing. Since 2019, Andrea has written over 90 blog posts and guides on sleep health, sleep hygiene, and product reviews. Find more articles by Andrea Comments Cancel replyLeave a CommentYour email address will not be published. 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