Memory foam, also referred to as visco-elastic foam, is a material known for its superior pressure relieving quality, which helps to reduce tossing and turning. It also provides even support by molding and contouring to the shape of your body, allowing for your spine to rest aligned, in its natural position. It is made from polyurethane, consisting of tiny molecules – cells, that under pressure release air and thus creating a unique molding feel. It softens in reaction to body weight and body heat.
Quality of memory foam is measured by its density - pounds per cubic foot (lbs/ft3). There is a great disparity in density/quality among manufacturers out there and it is our job to provide you with relevant information so you can make the right decision. Density of memory foam can vary between 2 to 6 lbs/ft3. Denser foams will be firmer, heavier, and more durable with shorter response time – faster recovery to its original shape. Higher quality foam mattresses will be made from at least 5lb/ft3, thus being quite heavy and more expensive.
Customers generally like the idea of memory foam being supportive, pressure relieving, durable, resistant to bacteria, mold, mildew, and mites. It reduces motion transfer across the mattress and provides the signature molding/melting feel. Some customers find memory foam warmer and difficult to turn around in it and there are numerous complaints about outgassing of the new mattresses causing respiratory irritation. High-density memory foam is not ideal for small children and adults with lower body weight, since their weight doesn’t’ allow for proper foam depression.
Lately, manufacturers are developing new forms of memory foam to eliminate excessive heat, improve response time or gain a certain marketing advantage by adding gel, latex-like components or natural ingredients.
What is memory foam?
Memory foam (visco-elastic foam) is an oil-based material, made from polyurethane with additional chemicals increasing its viscosity and density. It consists of tiny molecules – cells, that under pressure release air and thus creating a unique molding feel. In absence of pressure, cells refill with air and bounce back to its original shape – hence the name memory foam.
Quality of memory foam is measured by its density - pounds per cubic foot (lbs/ft3). Memory foam is typically denser and heavier than other polyurethane foams. Firmness is measured by a foam's indentation force deflection (IFD) rating but it is not a comprehensive measurement for determining the mattress firmness or softness. It needs to be compared relative to foam density.
It was designed by NASA in late 1960s to protect astronauts against extreme pressure at take off. It absorbs and disperses energy and reacts to weight and temperature. With these qualities it is more popular than ever with mattress manufacturers but it is becoming a go to material in other industries (shoes insoles, health care, sporting goods).
Types of Memory Foam
Traditional memory foam and its original formula was made popular by Tempur-Pedic and most mattresses nowadays are made from this foam but use different densities. The benefits are common among all types of memory foams but major differences are in heat absorption and response time, where traditional foam will retain more heat (though it might not be noticeable) and will have longer response time, so called “quicksand effect” especially with softer, lower density foams.
Gel memory foams are becoming more popular because they advertise the improvement on traditional memory foam drawbacks – heat retention and response time. Gel foam manufacturers claim that their foams are much cooler, but they don’t say by how much and this may not be even noticeable by an end-user. Gel foams are made by infusing gel molecules or by adding gel beets to memory foam giving the foam more resistance so you don’t sink in it too much and allowing gel particles to absorb excessive heat.
Other new types of memory foam, or next generation foams use similar approach as gel foams where they mix traditional foam with other chemical elements to improve response time, lower heat retention and provide a certain marketing advantage (natural ingredients). We have seen some soy, tea extract, based foams.
Some newer types of memory foam duplicate the construction of latex foam and contain deep holes throughout the entire layer to provide softer feel and also to help improve ventilation.
Quality and Density of Memory Foam
Some manufacturers are more transparent than other in providing foam specifications in their brochures or online. Memory foam quality is routinely measured by its density.
Density refers to the mass of one cubic foot of foam material. Typically, this value is given in feet - 4.0 lbs or 3.5 lbs/ft³. Memory foams that contain larger amounts of polymers and less air are denser and consequently weigh more and last longer. Most of the memory foams currently available you can assign to one of three categories:
Low Density – 2.0 lbs to 3.5 lbs
Medium Density – 3.5 to 5.0 lbs
High Density – 5.0 lbs to 8.0 lbs
Benefits of Memory Foam
Slower response time – molding feel
Long lifespan – up to 20 years
Construction of Memory Foam Mattress
Memory Foam mattresses, like any foam mattresses, are very simple in their construction, yet they can vary from one to another, especially in depth of the mattress and its components and in density these components are made from. There are typically few (2-6) layers of foam stacked or glued together. The bottom layer made from high-density polyurethane (referred to as the Core) is the thickest (4-8 inches) and firmest, providing support for the mattress. Top layers, one or more made from memory foam, are softer providing comfort and pressure relief.
The quality and price of the memory foam mattress depends on the construction of the core and type and density of memory foam used in top layers. High quality mattresses use high-density polyurethane core (6-8 inches) whereas lesser-quality products will either use thinner support layers (3-6”) or lower-density foam. Typical poly core would fall into one of following categories:
Regular Polyfoam (low)- under 1.8 lbs
High Density Polyfoam (medium) – 1.8 to 2.5 lbs
High Resiliency Polyfoam (high) – 2.5 lbs and up
To utilize the entire surface of the mattress and prevent rolling off the bed some manufacturers reinforce the sides of the mattress. Typically they incorporate walls of extra dense foam on both sides or all around the mattress. This design allows for keeping the body in the mattress instead of rolling off. Some manufacturers prefer not to use this type of edge construction because, as they claim, they favor consistent and uniform feel across the mattress.
The upper, comfort layers provide the mattress with softer feel and pressure relief and are typically made from traditional memory foam, gel foam, latex and lower density polyurethane foams. Top memory foam layer is usually 2-6” thick. Thicker layer will allow your body to sink more into the mattress, but using higher density foam can offset it. Higher quality products will typically use 4” or thicker memory foam layer of high-density foam - 5/lbs/ft3 or greater. This way they can provide exceptional combination of support and comfort with high quality foams, offering the best durability but at the much higher expense.
Memory Foam Manufacturing
Memory foam is produced in a complex multi-step process that takes several hours. Liquid chemicals are transported to the manufacturing facility in large tanks where they are mixed according to the proprietary formulas. The reaction process is called polymerization. After that the mass is poured into a mold on conveyor belt where it rises and cures. Then the foam is let to rest for several hours to allow proper curing. After curing is complete, the foam is trimmed into desired sizes.
Memory Foam Mattress Warranty
As the construction varies from model to model so does the warranty. Be extremely diligent to learn about the warranty of any given product. Warranties are design to protect consumer against manufacturer’s defects for certain period of time, and majority memory foam mattress warranties protect customers against excessive sagging. Excessive sagging is typically referred to as an indentation/imprint/depression greater than 1.5” for most of the mattresses, but memory foam mattress manufacturers consider indentation greater than 3/4" (some even ½”) as an excessive sagging under warranty. Most warranties start with a full mattress replacement for an initial period of time, and change to a limited (pro-rated) warranty as years go by. While comparing memory foam mattress warranties, you can find full replacement warranties for as little as 2 years and as high as 10 years, with overall warranty duration up to 25 years.
Be careful to read in between lines of marketing materials and product descriptions. Many of the so-called “memory foam mattresses” contain only a thin, low density layer of this foam, that doesn’t offer most of the advantages and benefits of memory foam. Higher quality foam mattresses will be made from at least 5lb/ft3, thus being quite heavy and more expensive. The denser the memory foam, the longer it will last, and the heavier it will be. Just like with any foam mattress if the product description doesn’t offer any density information try to lift it and “weigh” it relative to a different product.
Some sleepers feel that they retain too much heat, as traditional memory foam tends to store more body heat than other kinds of mattresses. Gel foam manufacturers claim that their foams are much cooler, but they don’t say by how much and this may not be even noticeable by an end-user. In general, memory foam material will always be warmer because it is right underneath your body to get you the desired molding feel. You can provide a breathing insulation barrier (thicker cotton mattress pad) to lower heat but it will also alter the overall mattress feel.
Memory foam mattress works well with partners of different body weights, where they don’t disturb each other, since it completely eliminates motion transfer (wine glass commercial). Memory responds slower and some customers experience what they call a "quicksand" effect, where they feel like they are stuck and locked in a position and is hard for them to move. Please keep these minor drawbacks in mind when deciding which memory foam type is right for you. As much as we believe memory foam mattresses are great products they provide very distinct feel that will not make everyone happy.
Be aware of different warranties, most of them covering indentations larger than 3/4” over certain period of time. Find out how long is the mattress fully covered, and if the warranty is pro-rated, know what portion of the replacement cost you will be responsible for. Make sure you ask your store about exchange/return options and exchange/return costs. Read the fine print of the exchange/return policy before you place an order.
Most stores will declare that they cannot offer any discounts on premium memory foam beds and that their prices are fixed by manufacturers. There is some truth to this but double check with more stores because some retailers are more lenient than others. Always ask for a special financing offers or the incentive for not using one. With some retailers extra delivery and old mattress removal fees can add to the final amount. Always ask for free gifts with a mattress purchase, it is always nice to get free pillows, mattress protector and set of sheets.