Whether you are deeply in touch with the modern mattress market (hello, r/Mattress posters) or haven’t bought a bed in over a decade, you’re likely at least a little familiar with memory foam. While its main association used to be with Tempur-Pedic, memory foam is everywhere now — in a seeming majority of mattresses (memory-foam mattresses, yes, but also most hybrids) as well as pillows and mattress toppers. But what exactly is it, and what’s the main reason you might want it in your mattress?
Memory foam is another name for viscoelastic polyurethane foam.
Lots of different polyurethane foams (also called polyfoams) are used across industries (in furniture, cars, aircraft, etc.), but what makes memory foam stand out from the others is that it’s viscoelastic. Having viscoelasticity means a substance has the viscosity of a fluid plus the elasticity of a gel or solid. To break that down, viscosity is the measure of a fluid’s resistance to a change in shape; think of how slow to change a thick, viscous liquidlike syrup is compared with water. Elasticity is the ability of a material to return to its original shape and size after pressure is removed. Put that all together, and it means memory foam is slow to change its shape but can return to its original shape when there’s nothing pressing on it anymore. You’ve likely seen this in action — in person or in an old commercial — when someone presses their hand into memory foam. The foam usually retains a handprint shape for a few seconds after the hand has been removed and then returns to its original shape. For this reason, memory foam is often called “slow-recovery foam.”
What exactly is memory foam made of?
Polyurethane foams, including memory foam, are made of three basic ingredients: a polyol, an isocyanate, and water. Water, we are all familiar with, but if you last took chemistry in high school, polyol and isocyanates may be unfamiliar. These ingredients mix together to cause the chemical reaction that creates foam. This reaction is almost instantaneous, like a superfast bread rising (in the foam-pouring industry, each piece is called a “bun,” furthering the yeasty comparison). Because of that quick chemical reaction, once the foam is poured, it’s not long before it rises to several feet tall — impressive since it starts as a liquid layer a few inches thick. After the foam fully rises, it is then stored, cured, and, later, cut and otherwise processed for use in mattresses (or any other memory-foam product). This method is called the “slabstock” production process; another common one is foam molding, in which the liquid mixture is poured into a mold instead of being allowed to rise into a bun. The molding technique is more common for products like contour pillows, which are molded into a specific shape, while the slabstock method lets foam producers create the large sections of foam used in the layers of a mattress.
What makes memory foam different from polyfoam — what gives it its viscoelastic nature — comes down to the exact formulation of the chemical mixture. Michael Crowell, executive director of the CertiPUR-US certification program, says those formulation changes can include things like using a higher-viscosity polyol and specific isocyanates. Crowell also says memory foam tends to be made at a higher density than other foams. While conventional polyfoam densities generally range around one to three pounds per cubic foot, memory-foam densities often start around three pounds per cubic foot and can go as high as eight, Crowell says.
Where did memory foam come from, and how did it end up in mattresses?
Polyurethane foams were introduced in mattresses in the 1950s after a shortage in American latex manufacturing left mattress companies looking for an alternative. In the 1960s, viscoelastic polyurethane foam was invented through the National Aeronautics and Space Administration’s Ames Research Technology Transfer Program and was originally intended as cushioning for astronauts. The slow-compressive qualities that made viscoelastic foam work as a comfortable cushion for space travel eventually made it a desirable material for relieving body pressure in mattresses. Though foams had been incorporated in mattresses for decades, not until 1992, when Tempur-Pedic launched in the United States, were most Americans introduced to “memory-foam mattresses.”
Whom is memory foam good for?
The main reason to get a mattress with memory foam is that you like the way it feels. Its slow-recovery, viscoelastic nature makes memory foam really good at relieving pressure and cradling the body. That means its cushioning can prevent the aches and pains that can easily form by sleeping on a material with less give — this is especially beneficial for side sleepers, who rest their body weight on their shoulder and hip while sleeping. It can also benefit back sleepers who want pressure relief around their lumbar area or shoulders. If you like to sink into your bed and you need pressure relief, memory foam is a pretty good bet.
But memory foam is also a pretty big category. Brands formulate their foam differently for different recovery times (e.g., five seconds to reform versus 15 seconds) and different densities, according to Crowell, which can make a big difference in the experience you’ll have on the mattress. This bears out in the variety of mattresses on the market — I’ve tested memory-foam mattresses that were soft and firm. It’s also worth noting that memory foam is incorporated into mattresses in a variety of ways. Even though there is a category commonly called “memory-foam mattresses,” these beds aren’t made entirely of memory foam. They typically use conventional polyfoam for a sturdy base and may use other foam formulations for the middle layers before finally adding actual memory foam in the top layers. Many hybrid mattresses use the same general construction format but substitute the polyfoam base layer with coils. So if you want memory foam, you aren’t limited to just “memory-foam mattresses” entirely made of foam; there are plenty of hybrids with equivalent amounts of memory foam.
What should I look for when purchasing a memory-foam mattress?
Clearly, there are a lot of factors to consider when choosing a memory-foam mattress. First and foremost, you’ll want to make sure the foams used in any mattress you purchase are CertiPUR-US certified. This certification covers the foam’s content, durability, and emissions. Essentially — and most important for a product you’ll be sleeping on every night — the certification means the foam is free of hazardous materials that could be used in foam production but shouldn’t be, owing to the harm they may cause to human health and/or the environment. Brands will usually advertise that they have the certification, but best practice is to double-check in the online directory.
If you really want to dig into the details of the foam in a mattress, you can also look at foam performance factors, such as the foam’s density and firmness. Memory foam does tend to have a higher density than polyfoam, but the densities can range a lot. Foam density is generally measured in pounds per cubic foot. The higher the density of the foam, the more durable and supportive it will feel. But a higher density also means a higher price. High-end brands like Tempur-Pedic that use high-density foams are likely to charge a higher price to the customer because the foam costs more to produce; conversely, you probably won’t get high-density foam in ultrabudget mattresses. If durability and quality are big concerns for you, look for high-density foam but expect to pay for it.
While it may seem as if a dense foam would also be firmer, that’s not necessarily the case, Crowell told me. High-density foam can be firm, soft, or somewhere in the middle, as can lower-density foams. So what is firmness exactly? It’s measured by indentation force deflection, sometimes called indent load deflection. This is a measurement of the force in pounds needed to indent a foam sample by 25 percent of its original height, according to the Polyurethane Foam Association. What you really need to know is that the higher the IFD/ILD, the firmer the foam — i.e., more pounds of pressure are required to indent it. According to FoamOnline, most foams range between 15 and 70 IFD/ILD. Admittedly, this information isn’t always readily available when you’re shopping for a mattress, so if you really want to know, you may need to ask a salesperson or reach out to a brand directly.
The last thing you’ll want to consider are heat-combating infusions, which all fall under the umbrella term phase-change materials. These can include gel, copper, and graphite, which are infused into the foam to counteract some of its heat-trapping nature. These materials act as a heat sink: When the beads of gel (or copper or graphite, etc.) are squished together as your body compresses the foam, they absorb your body heat; then the heat transfers to other beads in the foam and slowly disperses away from you. This, chemist Neil Silverman from 3Z Brands explained to me, is why these infused foams don’t necessarily feel cool. Rather, they disperse heat away from you to regulate temperature.
Whom is memory foam not good for? What alternatives are there?
If memory foam doesn’t appeal to you, there are other options. Some reasons you might want an alternative include memory foam’s lack of bounce or responsiveness, its heat-trapping nature, and the way it allows the body to sink in rather than stay “on top” of the bed. You may also want to avoid memory foam if you prefer not to buy plastic-based products since it is ultimately derived from petrochemicals. Let’s break those down.
First, the lack of bounce or responsiveness: Memory foam’s slow-recovery nature means it doesn’t offer much bounce. For some people, this isn’t much of an issue, but if you like a bed with a little bounce, you want to be able to easily toss and turn at night, or you want a bed that’s good for having sex on (hey, it’s worth considering!), then slow-sinking memory foam may not be ideal. For something more responsive, I would recommend latex foam. It’s similar to polyurethane foam but is derived from rubber-tree sap. It’s thus much bouncier and has a quicker response time than memory foam does — most latex products I’ve tried bounce back instantly. Some polyurethane foams out there do have the latexlike quality of bouncing back quickly; these are usually referred to broadly as “latex alternatives” but often have branded names such as Energex. Similarly, latex and latex alternatives will probably be your best bet for staying more on top of the bed rather than sinking in.
As far as heat goes, latex is likely the best one-for-one swap. I usually find latex feels cooler than memory foam, though it’s worth noting the difference isn’t drastic. Latex is often hole-punched for ventilation (which you can do with memory foam, too, but it seems more common with latex). However, you could opt for memory foam with some of the cooling infusions I mentioned above if you are otherwise okay with the material. I also tend to advise picking a mattress with springs since there’s a lot more room for airflow in such a mattress — this could be a memory-foam hybrid or any other style of hybrid or innerspring mattress.
Finally, if ecofriendliness is your main concern, there are some alternatives. Latex is most commonly cited as an environmentally friendly choice instead of memory foam since the base material for latex is a renewable resource (sap from rubber trees) versus the nonrenewable petrochemical base material in memory foam. It’s important to note, though, that some synthetic latexes are also made from petrochemicals, so look for natural or organic latex. Another more ecofriendly option is “bio-based” foams. These are generally still partially petroleum based but also contain some bio-based content (such as soy or castor oil). Bio-based foams can be made as conventional polyfoam or viscoelastic, so technically they could fall under the category of memory foam. However, I’m defining them separately since they are usually advertised as being distinct from it.
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