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Memory foam is polyurethane with additional chemicals increasing its viscosity and density. It is often referred to as "visco-elastic" polyurethane foam, or low-resilience polyurethane foam (see LRPu). Higher-density memory foam softens in reaction to body heat, allowing it to mold to a warm body in a few minutes. A lower-density memory foam is pressure-sensitive and molds quickly to the shape of a body pressing against it, returning to its original shape once the pressure is removed.[clarification needed] Faster speed of recovery of a foam to its original shape after a weight is removed is sometimes claimed as an advantage by memory-foam mattress producers, who may talk of "newer generation" foams with "faster recovery."
Memory foam was developed in 1966 under a contract by NASA's Ames Research Center to improve the safety of aircraft cushions. Ames scientist Chiharu Kubokawa and Charles A. Yost of the Stencel Aero Engineering Corporation were major contributors to this project. The temperature-sensitive memory foam was initially referred to as “slow spring back foam”; Yost called it "temper foam". Created by feeding gas into a polymer matrix, the foam has an open-cell solid structure that matches pressure against it, yet slowly springs back to its original shape.
Yost later founded Dynamic Systems Inc. in collaboration with NASA to commercialize the foam, including it in both medical equipment such as X-ray table pads and sports equipment such as football helmet liners. After Dynamic Systems sold memory foam products to Becton, the range of products was expanded.
When NASA released memory foam to the public domain in the early 1980s, Fagerdala World Foams was one of the few companies willing to work with the foam, as the manufacturing process remained difficult and unreliable. Their 1991 product, the "Tempur-Pedic Swedish Mattress" eventually led to the mattress and cushion company, Tempur World.
Memory foam was subsequently used in medical settings. For example, it was commonly utilized in cases where the patient was required to lie immobile in their bed on a firm mattress for an unhealthy period of time. The pressure over some of their body regions decreased or stopped the blood flow to the region causing pressure sores or gangrene. Memory foam mattresses significantly decreased such events.
Memory foam was initially too expensive for widespread use, but became cheaper. Its most common domestic uses are mattresses, pillows, and blankets. It has medical uses, such as wheelchair seat cushions, hospital bed pillows and padding for persons suffering long-term pain or postural problems; for example, a memory foam cervical pillow may alleviate chronic neck pain. Its heat-retaining properties may help some pain sufferers who find the added warmth helps to decrease the pain.
Unfortunately, the heat-retaining properties can also be a downside when used in mattresses and pillows so in the 2nd generation memory foam, companies began using open cell structure to better help with breath-ability. In 2006, the 3rd generation of memory foam was introduced. Gel visco or gel memory foam, consists of gel particles fused with visco foam to reduce trapped body heat, speed up spring back time and help the mattress feel softer. It was jointly developed by Dynamic Systems Inc. and Thurmo-Pudic USA. Although various bedding companies experimented with the material, gel mattresses did not become popular until the introduction of Serta’s iComfort line in 2011.
Since the development of gel memory foam, other materials have been added. Aloe vera, green tea extract and activated charcoal have been combined with the foam to reduce odors and even provide aromatherapy while sleeping. Bamboo fiber has been used in woven mattress covers over memory foam beds to wick moisture away from the body to increase comfort.
A memory foam mattress is usually denser than other foam mattresses, making it both more supportive, and heavier. Memory foam mattresses are often sold for higher prices than traditional mattresses.
The property of firmness (hard to soft) of memory foam is used in determining comfort. Firmness is measured by a foam's indentation force deflection (IFD) rating. However, it is not a complete measurement of a "soft" or "firm" feel. A foam of higher IFD foam but lower density can feel soft when compressed.
IFD measures the force (in pounds-force) required to make a dent 1 inch into a foam sample 15" x 15" x 4" by an 8-inch-diameter (50 sq in) disc—known as IFD @ 25% compression. IFD ratings for memory foams range between super soft (IFD 10) and semi-rigid (IFD 120). Most memory foam mattresses are firm (IFD 12 to IFD 16).
Some [according to whom?] report that IFD is a poor way to measure softness of memory foam, and that foam density as a measure of quality is more important, but not always true. Foam density of 5 pounds per cubic foot (80 kg/m3) or greater is considered high quality, although most standard memory foam has a density of 1 to 5 lb/ft3 (16–80 kg/m3). Most bedding, such as topper pads and comfort layers in mattresses is 3 to 4.5 lb/ft3. Very high densities such as 5.3 lb/ft3 (85 kg/m3) are used infrequently in mattresses.
The new 2nd and 3rd generation Memory foams have an open-cell structure that reacts to body heat and weight by 'molding' to the sleeper's body, helping relieve pressure points, preventing pressure sores, etc. Most memory foam has the same basic chemical composition, however the density and layer thickness of the foam makes different mattresses feel very different. A high-density mattress will have better compression ratings over the life of the bedding. A lower-density one will have slightly shorter life due to the compression that takes place after repeated use.
When new, some memory foams give off a distinct chemical odor, which many [according to whom?] people find unpleasant and some [according to whom?] say is akin to the smell of paint. This odor decreases with airing, but some people [according to whom?] remain sensitive. Emissions from memory foam mattresses may directly cause more respiratory irritation than other mattresses; however mildew and house dust mites may not occur as frequently, so asthma attacks may be less frequent and severe.
Certain 3rd Generation Bamboo-Infused Memory Foam mattresses are now certified 100% Toxin Free. These mattresses typically cost extra, but prevent any kind of off-gassing or emissions which could potentially be dangerous for those with allergic reactions (see health concerns below).
Memory foam, like other polyurethane products, can be combustible. Laws in several jurisdictions have been enacted to require that all bedding, including memory foam items, be resistant to ignition from an open flame such as a candle or cigarette lighter. US bedding laws that went into effect in 2010 change the Cal-117 Bulletin for FR testing. There is concern that high levels of the fire retardant PBDE, commonly used in memory foam, could cause health problems for users. PBDEs are no longer used in most bedding foams, especially in the European Union.
Manufacturers caution about leaving babies and small children unattended on memory foam mattresses, as they may find it difficult to turn over, and may suffocate.
The United States Environmental Protection Agency published two documents proposing National Emissions Standards for Hazardous Air Pollutants (HAP) concerning hazardous emissions produced during the making of flexible polyurethane foam products. The HAP emissions associated with polyurethane foam production include methylene chloride, toluene diisocyanate, methyl chloroform, methylene diphenyl diisocyanate, propylene oxide, diethanolamine, methyl ethyl ketone, methanol, and toluene however not all chemical emissions associated with the production of these material have been classified. Methylene chloride makes up over 98 percent of the total HAP emissions from this industry. Short-term exposure to high concentrations of methylene chloride also irritates the nose and throat. The effects of chronic (long-term) exposure to methylene chloride in humans involve the central nervous system, and include headaches, dizziness, nausea, and memory loss. Animal studies indicate that inhalation of methylene chloride affects the liver, kidney, and cardiovascular system. Developmental or reproductive effects of methylene chloride have not been reported in humans, but limited animal studies have reported lowered fetal body weights in rats exposed.
See also 
- Nelles, Barbara. "Exhibitors emphasize value pricing in Vegas Foam trends, adjustables and top-of-bed also make news." BedTimes Magazine. November 2009. Retrieved 2011-8-26.[dead link]
- NASA spinoff database
- COSMOS Magazine
- Your Gel Mattress - Get Comfortable by Sleeping Like a Cow
- Polyurethane Foam Association - Density Standards and Guidelines
- Anderson RC, Anderson JH, Respiratory toxicity of mattress emissions in mice, Archives of Environmental Health, Jan-Feb 2000
- Memory Foam MSDS Sheet
- California Bureau of Home Furnishings and Thermal Insulation
- Arlene Blum The Fire Retardant Dilemma. Science. 12 Oct 2007: 194b-195b.
- Federal Register / Vol. 61, No. 250 / Friday, December 27, 1996 / Proposed Rule: Environmental Protection Agency and Environmental Protection Agency Federal Register / Vol. 63, No. 194 /Wednesday, October 7, 1998 /Rules and Regulations
- Environmental Protection Agency Federal Register / Vol. 63, No. 194 /Wednesday, October 7, 1998 /Rules and Regulations