Memory Foam Density

Density is a concept that can be tricky to understand when shopping for a memory foam mattress, but it remains one of the most important features to check before splurging on a new bed. While memory foam density can’t tell you everything about a mattress, it does play an important role in both durability and comfort.

Amerisleep's Dr. Bed Head explains density

Why is Memory Foam Density Important?

Density is the weight of one cubic foot of memory foam (a 12 inch cube). Density differs as a result of the materials used in the foam construction, and the amount of polymers versus air present in the product. The common range of densities for memory foam is between 2.5 pounds and 7.0 pounds. Generally speaking, foams below 3.5 lbs are considered low density, foams between 3.5 and 5.0 lbs are considered medium density, and foams over 5.0 lbs are considered high density (though definitions can vary by brand). Lower density foams are cheaper to produce because they require less material, and thus (typically) cost less.

Density of memory foam is the weight of one cubic foot

When shopping for a memory foam mattress, it is important to find out what the density of each layer is. For one, you want to make sure the retailer knows about the product they are trying to sell you. But more importantly, you want to make sure that the bed you are looking it is worth price, and falls in line with your needs and expectations. Density can also be important when comparing different brands and models to get an idea of value.

When shopping for memory foam, know what the density of each layer is

Density & Durability

While not the only indicator of quality, density does have an affect on the overall lifespan of the memory foam. Low density memory foam tends to soften and break down at a faster rate than medium and high density foams2. This loss of support and resiliency decreases the useful lifespan of the mattress. On average, one can expect a low density memory foam bed to last around 5 years, whereas medium density memory foam lasts 7-8 years and high density foams last 9-10 years1. Because a lifespan plays a critical role in value, this is important. Even though a low density mattress may be cheap, it might need to be replaced twice as often as mattress with medium or high memory foam density.

Density has an affect of the lifespan of memory foam

Density & Comfort

Memory foam density also has significant implications for comfort as well, specifically in the feel of the memory foam, heat retention, and odor. High density foams tend to feel very viscous, especially temperature sensitive varieties. This can result in a sensation that some describe as being stuck in a hole or trapped in quicksand, making changing positions or getting of bed difficult, and also reducing enjoyment of nighttime activities. Less dense foams are less viscous, and thus tend to receive fewer complaints regarding difficulty moving.

Sleeping hot is an important concern for many mattress shoppers, and memory foam density can play a role. Denser foams are more likely to trap heat, since the internal structure of the foam allows less air through. In general, less than 5% of owners of low density memory foam beds complain of heat versus over 12% of those with high density beds1. In the same regard, about 15% of those who own high density memory foam beds complain of odor, versus 7% with mattresses of low memory foam density.

Higher density memory foam is harder to move on, while less dense material is less viscous

Memory Foam Density vs. Support Core Density

The density of all the layers in a memory foam mattress should be considered when researching beds. Memory foam mattresses typically consist of one or more layers of memory foam over a foam core, and may also include other types of foam as well. Mattress cores have different rules when it comes to density, as these are designed to support the sleeper and are not viscoelastic. Good density for foam support core is around 2.0 pounds. Lower densities will breakdown earlier and provide less support.

An ideal density for support memory foam is between 2.0-2.5 lbs

What Memory Foam Density Can’t Tell You

Firmness

Density and firmness are not necessarily related. You can find both low-density and high-density beds that range from soft to firm. Firmness depends more on the firmness of the foam itself, depth of memory foam, the layers used in the mattress, and the ambient temperature (for temperature sensitive foams).2

Density isn't directly realted to the firmness of memory foam

Comfort

All types of memory foam generally receive good reports of comfort, at least in the first few years. Different people will also prefer different types of beds, so no one density will be universally comfortable.1

People prefer different feel when it comes to memory foam

Motion Isolation

All memory foam densities tend to prevent motion transfer between couples equally well.1

Customers with memory foam report no motion transfer between partners

Comparing Memory Foam Density

As you can see, density plays an important role in memory foam mattresses, and understanding the concept and how it affects a product can be helpful when looking for the best bed. Keep in mind that not all expensive beds have desirable densities and vice versa. Price depends on brands, market and other factors, so be sure to look “under the covers” rather than relying on a brand or price tag to speak for quality. Always ask for detailed specifications when shopping, including core and memory foam density, so you can make effective comparisons and find the right mattress for your needs.

Density
Low (3.5 lbs or less)
Medium (3.5-5.0 lbs)
High (5.0 lbs or more)
Average Lifespan
5 years
7-8 years
9-10 years
Average Heat Complaints
5%
8%
12%
Average Odor Complaints
7%
10%
15%

Resources:

1http://www.sleeplikethedead.com

2http://www.pfa.org/jifsg/jifsgs1.html

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