About Polyurethane & Memory Foam
Virtually all mass market mattresses feature significant quantities of polyurethane or memory foam, making this article an excellent resource in helping to understand what these materials are all about.
This is an in-depth article of approximately 2,500 words. The links below skip directly to various sub-topics.
What is Polyurethane Foam?
Polyurethane foam is the most common upholstery material used in mattresses, sofas, car seats today. It is used in both all foam as well as spring/coil mattresses as almost all of the upholstery foam used over the springs is of this type of foam that is used in all common mass produced mattresses. Standard polyurethane foam typically is the source of most softening (low resilience), loss of support (low elasticity) in a mattress, as well as a significant amount of body indentation; this is particularly true when speaking of the lower density polyurethane foams (0.8~1.8 lbs/ft3) used in softer pillowtop mattresses which are known to have a limited life span. Our goal is not to demonize this material, the truth is; comfortable mattresses are less expensive today than they have ever been and it is in large part due to the endemic use of polyurethane foams. It is however our opinion that these materials should not be used extensively in any higher priced products on the market. Particularly if the mattress is not flippable or the polyfoam layers removeable and replaceable in a modular mattress design, both features that are uncommon today.
Polyurethane is a polymer material made from reacting different monomer materials; isocyanates and polyols both derived from refined crude oil. Polyurethane foam is the most common upholstery material used today. It is found in almost all mattresses, sofas, the seats in your car, spray foam insulation and more. The main chemical ingredient is made of an isocyanate (toluene diisocyanate or methyl diphenyl diisocyanate being the most common). These chemicals makes up approximately two thirds of the weight of the finished foam.
One third of the finished weight of memory or poly foam is created from Polyols. This is a form of alcohol, which is almost always made entirely from petrochemicals. There are some polyols containing plant based alcohols (soy, castor bean, tea tree, aloe, et cetera), in very small percentages. These foams are often labelled as natural, which we feel is entirely misleading as the vast majority of the finished product is not natural and there is zero health related benefit to using plant polyols in polyurethane foam production.
The other critical part of making all polyurethane foam is a blowing agent. This is a chemical in the form of a gas which is blown into the mixture to turn it into foam, essentially aerating the mix. Different types of polyurethane and memory foams simply use different blowing agents. Some foams are water expanded, which is another clever way of suggesting that somehow the foam is natural. This is simply green washing. The process of making polyurethane is typically not as sophisticated as most would think. Although there are other methods for making ‘continuous’ pieces of foam on more expensive machinery the crude single batch method in the video below can produce foam of the same quality.
Video of Polyurethane Foam Production
What is Memory Foam?
Simply stated, memory foam is polyurethane foam. Essentially, there are different primary ingredients involved in the mixture, and different blowing agents in the foaming process. Memory foam may also be called viscoelastic foam.
Memory foam is an improvement upon standard polyurethane as it is more durable and also offers moderately improved pressure relief and support. The enhanced durability is not because of the "memory" and is actually a result of the density of the material. Typical polyurethane foam used in mattresses is 0.8 to 1.8 lbs/ft3 while most memory foam is 3.0 to 5.0 lbs/ft3.
The "memory" in memory foam is actually due to the 'viscoelastic' nature of memory foam versus traditional polyurethane foam. Both varieties of foam will try to return to their original shape. Memory foam and polyurethane foam do break down over time. There is actually strong evidence that shows memory foam actually needs to be higher density to match the real world durability of standard polyurethane foam. The difference is that memory foam is typically quite a bit higher density than run of the mill comfort layers made of low density polyfoam so they do last longer on average. A high quality memory foam mattress usually provides 6-8 years of optimal support and comfort compared to the average life span of 3-5 years for traditional pillow top-variety mattresses.
Memory foam is too low in elastic response to be considered a support material, memory foam is a comfort/pressure relieving material; this is why you will never see a memory foam mattress that is memory foam from top to bottom. Typically 2-5" of memory foam is used over the top of polyurethane foam cores which gives a bit of resilience and support. This is fine to use polyfoam cores in lower cost mattresses, however standard polyurethane foam used in the core of these mattresses is fairly rigid and not comfortable or elastic it requires thicker layers of memory foam. It is also somewhat common to find 0.5" or 1.0" thick layers of memory foam in the tops of coil mattresses, however the vast majority of these mattresses still use a significant amount of lower density polyurethane foam in the construction which will the same pitfalls.
Here at TMASC we really believe in the elastic bed principle. It is far more optimal in terms of support to use thinner layers of memory foam (3" or less) over the top of a more elastic and supportive core than polyurethane foam. Individual pocket springs or latex foam both work excellently underneath the top layers of memory foam. These support systems are more flexible and comfortable than standard polyurethane foam which allows thinner layers of memory foam to be used in order to get the desired comfort and pressure relief necessary. This also has the very desirable effect of maintaining proper support by the body being closer to a more elastic and supportive base of the mattress. This also increases breathability through the core of the mattress, as well as increases the functional life span as these cores will not lose resiliency and support nearly as quickly as a cheaper low density polyurethane foam core. In some cases, our memory foam and pocket spring mattresses are often less expensive and higher quality than the standard big brand name memory foam mattresses available.
Usable life spans are merely averages. For every person finding 8 years of good support from their memory foam mattress there would be just as many receiving only 2 years. On a daily basis we encounter folks who are replacing their pillow top or polyurethane/memory foam upholstered mattress in as little as 6 or 12 months.
What is HR Foam?
HR or high resiliency foam used to be more common decades ago but is typically hard to find now. If you know of someone who once owned a comfortable and long lasting foam mattress that was not made of memory foam or latex, chances are it is the very uncommonly used HR foam. These foams are typically characterized by a much higher density and elasticity than standard polyurethane foams, 2.5 lbs/ft3 is typically minimum and the best ones are typically over 3.0 lbs/ft3 which actually can be very long lasting as a comfort material. The increased elasticity of this foam also makes it far more supportive and functional for use in a mattress than standard polyurethane foam. We do have access to this higher quality HR foam and it can be used for excellent value.
Polyurethane Foam Durability
To simplify, the more dense polyurethane or memory foam is, the more durable it will be. The challenge with regular polyurethane foam is that as we increase the density, it can become rigid and hard which many find to be uncomfortable. This is the primary reason why most high density polyurethane foams are of the memory foam variety. Memory foam is more apt to offer additional flexibility and forgiveness as the density increases. The exception to this rule is rarely used HR polyurethane foam, which is made of slightly different chemicals and can be made in higher densoities while still being supple and supportive. We use this special HR 3.4lb density foam in the top of our Tranquil mattress.
The limitations of this material in relation to density results in the vast majority of mattresses and sofas being made with low-density foam in an effort to ensure these products are comfortable to use. The issue is that this is the least durable way to upholster such products. The optimal support of mattresses and sofas with large quantities of low density foam is often measured in months and not in years.
Is Polyurethane Foam Flammable?
Whether intentional or not, many mattress salespersons will wrongfully inform their customers that mattresses are not treated with chemical flame retardants. This is simply untrue. As all forms of polyurethane foam are made up of hydrocarbons, they are exceptionally flammable. Thus, chemical additives are required to ensure the foam is less combustible.
Formaldehyde is the most common chemical flame retardant used in mattresses containing polyurethane or memory foam. This is because formaldehyde is abundant and very inexpensive. Less common today than it was even just 5 years ago PBDE's (polybrominated diphenyl ethers) can also be used as fire retardants in polyurethane foam; PBDE's are less common now than formaldehyde based fire retardants as they are known to bio-accumulate in breast milk, blood and fat tissues. This is a major concern as PBDE's can affect the brain and nervous system while in developmental years, as well as disrupting the thyroid and estrogen hormonal balance in humans. For any polyurethane foam that is actually produced in North America PBDE’s are now banned from use in production. However, some polyurethane foam products that are imported from other regions often do still use PBDE’s as a fire retardant.
If you have concerns about chemical flame retardants we suggest reading the law tag on the mattress. Even though there are no specific requirements for listing the chemicals inside the mattress, there is fortunately a law requiring the finished components to be listed on the tag. Thus, all we need to look for is "polyurethane foam." If this material is listed on the law tag, the mattress contains chemical flame retardants. It truly is this cut and dry, regardless of claims made by retailers or manufacturers.
There are alternative means of meeting fire safety regulations such as using Kevlar, boric acid, saline solutions, et cetera. Natural mattresses use sheep's wool in the external quilting layers of a mattress to provide a natural fire barrier.
Polyurethane Foams & Memory Foams Are Sensitive to Moisture
Moisture will speed up the degradation of all polyurethane and memory foams. It is important to keep moisture out of this material and to ensure the area around the material may breathe and have adequate air circulation. In the case of caring for your mattress, using natural materials such as sheep's wool is very important.
What is Natural Memory Foam?
There are two categories of "natural memory foam"
One variety of natural memory foam is actually a slow-response latex foam aggressively marketed as "natural." This slow responding latex foam contains additional chemical additives needed to inhibit the slower, "memory foam" type of responsiveness. This material does contain some natural content; however it still contains styrene and butadiene. These two chemicals are both volatile organic compounds (VOC's) and as such we feel it is inappropriate to market this foam as "natural memory foam." One must simply read the ingredients list to verify these two VOC's are present in this "natural memory foam."
This foam has been independently lab tested showing that the finished material contains approximately 3% bio based ingredients. However, the mean result is +/- 3%, which indicates the material tested is either as much as 6% natural based material or as little as 0%. PDF of Lab Report
On July 25, 2013 the Federal Trade Commission in the United States barred three different companies from advertising mattresses as free from VOC's. View the report here.
Some polyurethane foams incorporate plant alcohol in the chemical mixture. These sources can be soy beans, caster beans, tea tree, aloe and many others. As we touched on earlier, it is important to remember that these polyols can only be a very small percentage of the finished product. Although marketed as natural, we feel this is inappropriate. The Mattress & Sleep Company simply labels these foams as "Plant-based foam" to denote that in the products we offer with this material, a portion of the polyol has been replaced by a plant-based alcohol.
The only truly all-natural foam available today is natural rubber tree latex.
Does Polyurethane Foam Produce an Odour?
Yes. All varieties of polyurethane foam (including memory foam) produce an odour. All plant-based polyurethane foams (soy, castor bean, tea tree, aloe, etc) produce an odour, regardless of product claims.
This odour is commonly referred to as "off-gassing." The odour will dissipate with time. As each person is different, sensitivity to off-gassing will vary. For those concerned about this, having 3rd party certification from CertiPUR-US can bring some peace of mind, mattresses made only of foams certified by this company tend to have a lot less odour and are free of any known harmful emissions. Most of the foam products we sell carry this label with only a few exceptions, but is listed on all of our product pages where applicable. In truth the actual chemical off-gassing will never go away completely. If you are concerned about off-gassing, natural rubber tree latex foam is an alternative which does not contain harmful chemicals to any significant extent.
Note: Natural rubber tree latex foam also has an odour, although the key difference is that this odour is naturally occurring. This odour is not offensive for the overwhelming majority of our clients and is almost never noticeable unless you are inspecting the rubber without coveringsNatural rubber should not be confused with synthetically blended latex foam, which although may be considered "low VOC" by some measurements is still made from various petrochemical sources. The key consideration for those with multiple chemical sensitivities (MCS) is to avoid products which emit high levels of VOC's.
Does Polyurethane Foam Sleep Hot?
Yes. Polyurethane foam (including memory foam) is primarily a closed-cell foam. This means that neighbouring cells are walled off from each other, which does not allow much airflow. Although certain memory foams claim to be open-cell, the level of breathability in the real world is minimal. See the video below comparing the Vita Talalay latex found in our Berkeley Ergonomics mattresses compared to the most popular memory foam on the market.
This lack of airflow causes polyurethane foam to retain a great deal of heat. When a mattress is hot, the sleeper perspires more, disrupting deep sleep. Only a small number of polyurethane foam mattresses incorporate wool or other breathable natural fibres, and most of the time, these natural fibres are 5-10% of the overall blend, with the rest being polyester. Cooling gel technology can make a small difference but absolutely does not solve for this lack of breathability, the solutiuon is proper bedding
The Mattress & Sleep Company offers a variety of bedding products designed to help alleviate temperature concerns with memory foam mattresses. It is common to add natural fibres to a foam mattress to improve airflow. The number one solution to this problem is the St. Dormeir mattress protector, we recommend these for any mattress made of polyurethane foam for maximum breathability, moisture wicking and overall sleeping comfort.
When we sleep too hot, we perspire. How your mattress and bedding deal with this moisture is critical. This is why the optimal sleeping environment should incorporate layers of natural animal fibres such sheep's wool, alpaca, horse tail or camel hair. These natural fibres hold between 25 and 40% of their weight in moisture, whereas synthetic foams and fibres such as polyester can typically only absorb up to 1% of their weight. Also, natural animal fibres are scientifically proven to regulate temperature and steady the heart rate.
Another contributing factor to sleeping hot is that most mattress stores convince their customers to purchase a waterproof mattress protector. The issue here is that no matter what the marketing message claims, a waterproof mattress protector isn't very breathable. What ends up happening is that with minimal air circulation, you overheat easily and then your body perspires more to try and cool down. This moisture has nowhere to go since you're right up against a waterproof layer. This leads to a clammy feeling, which severely fragments sleep.
Waterproof mattress protectors should only be used when it is absolutely necessary. As a healthy alternative, The Mattress & Sleep Company offers both a Natura wool puddle pad and a Obasan organic wool puddle pad, which are very-nearly waterproof, yet crafted only from pure sheep's wool which will still regulate temperature and humidity while providing excellent moisture protection for your mattress.
Perhaps most important of all, your mattress protector, sheets, duvet and pillow all play just as significant a role in your sleeping temperature as does the mattress.