Memory foam
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Memory foam consists mainly of polyurethane with additional chemicals that increase its viscosity and density. It is often referred to as "viscoelastic" polyurethane foam, or low-resilience polyurethane foam (LRPu). The foam bubbles or ‘cells’ are open, effectively creating a matrix through which air can move. Higher-density memory foam softens in reaction to body heat, allowing it to mold to a warm body in a few minutes. Newer foams may recover their original shape more quickly.[1]
Mechanics
Memory foam derives its
- The pneumatic effect, caused by the time it takes air to flow into the foam's porous structure.
- The adhesive effect, or adhesion, caused by the stickiness of the surfaces within the foam, which work against decompression as the internal pores within the foam are pressed together
- The relaxation effect (the strongest of the three forces working against expansion), caused by the foam's material being near its glass transition temperature—limiting its mobility, forcing any change to be gradual, and slowing the expansion of the foam once the applied pressure has been removed
The effects are temperature-dependent, so the temperature range at which memory foam retains its properties is limited. If it is too cold, it hardens. If it is too hot, it acts like conventional foams, quickly springing back to its original shape. The underlying physics of this process can be described by polymeric creep.[2][3]
The pneumatic and adhesive effects are strongly correlated with the size of the pores within memory foam. Smaller pores lead to higher internal surface area and reduced air flow, increasing the adhesion and pneumatic effects. Thus the foam's properties can be controlled by changing its cell structure and porosity. Its glass transition temperature can also be modulated by using additives in the foam's material.[2]
Memory foam's mechanical properties can affect the comfort of mattresses produced with it. There is also a trade-off between comfort and durability. Certain memory foams may have a more rigid cell structure, leading to a weaker distribution of weight, but better recovery of the original structure, leading to improved cyclability and durability. Denser cell structure can also resist the penetration of water vapor, leading to reduced weathering and better durability and overall appearance.[4]
History
Memory foam was developed in 1966 under a contract by NASA's Ames Research Center to improve the safety of aircraft cushions. The temperature-sensitive memory foam was initially referred to as "slow spring back foam"; most called it "temper foam".[5] Created by feeding gas into a polymer matrix, it had an open-cell solid structure that matched pressure against it, yet slowly returned to its original shape.[6]
Later commercialisation of the foam included use in medical equipment such as X-ray table pads, and sports equipment such as American / Canadian football helmet liners.
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 it, 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, when patients were required to lie immobile in bed, on a firm mattress, for an unhealthy period of time, the pressure on some of their body regions impaired blood flow, causing
Memory foam was initially too expensive for widespread use, but became cheaper. Its most common domestic uses are mattresses, pillows, shoes, and blankets. It has medical uses, such as wheelchair seat cushions, hospital bed pillows and padding for people suffering long-term pain or postural problems.
Gel
Heat retention can be a disadvantage when used in mattresses and pillows, so in second-generation memory foam, companies began using open cell structure to improve breathability.
In 2006, the third 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. This technology was originally developed and patented by Peterson Chemical Technology,[8] and gel mattresses became popular with the release of Serta's iComfort line and Simmons' Beautyrest line in 2011. Gel-infused memory foam was next developed with what were described as "beads" containing the gel which, as a phase-change material, achieved the desired temperature stabilization or cooling effect by changing from a solid to a liquid "state" within the capsule. Changing physical states can significantly alter an element's heat absorption properties.
Since the development of gel memory foam, other materials have been added.
Mattresses
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. Memory foam used in mattresses is commonly manufactured in densities ranging from less than 24kg/m3 (1.5 lb/ft3) to 128kg/m3 (8 lb/ft3) density. Most standard memory foam has a density of 16–80 kg/m3 (1 to 5 lb/ft3). Most bedding, such as topper pads and comfort layers in mattresses, has a density of 48–72 kg/m3 (3 to 4.5 lb/ft3). High densities such as 85 kg/m3 (5.3 lb/ft3) are used infrequently.
The firmness property (hard to soft) of memory foam is used in determining comfort. It is measured by a foam's
IFD measures the force in
Second and third 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.
Memory foam mattresses retain body heat, so they can be excessively warm in hot weather. However, gel-type memory foams tend to be cooler due to their greater breathability.[13]
Hazards
Emissions from memory foam mattresses may directly cause more respiratory irritation than other mattresses. Memory foam, like other polyurethane products, can be combustible.[14] 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.[15]
There is concern that high levels of the fire retardant
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.[13]
The
See also
References
- ^ Nelles, Barbara. "Exhibitors emphasize value pricing in Vegas Foam trends, adjustables and top-of-bed also make news Archived 2014-02-03 at the Wayback Machine." BedTimes Magazine. November 2009. Retrieved 2020-12-29.
- ^ a b Krebs, Michael. "The Adjustment of Physical Properties of Viscoelastic Foam – the Role of Different Raw Materials" (PDF). pu-additives.com. Retrieved 21 May 2020.
- ^ Landers, R. "The Importance of Cell Structure for Viscoelastic Foams" (PDF). pu-additives.com. Retrieved 21 May 2020.
- .
- ^ a b "spinoff 2005-Forty-Year-Old Foam Springs Back With New Benefits". nasa.gov. Archived from the original on 20 March 2009.
- ^ ""Eight spin-offs from space" Article from Cosmos Magazine". The Healthy Foundations Blog. Archived from the original on 2014-02-01. Retrieved 2014-01-25.
- PMID 8407250.
- ^ Peterson, Bruce W. "Mr". Polyurethane Gel-Like Polymers, Methods and Use in Flexible Foams. Archived from the original on 2014-04-19. Retrieved 2014-04-18.
- PMID 30966151.
- ^ "Polyurethane Foam Association". pfa.org. Archived from the original on 2010-01-04. Retrieved 2010-01-15.
- ^ Strand, Andrea. "Memory Foam Mattresses Guide For Side Sleepers". Retrieved 17 August 2018.
- ^ Annie Stuart (2010-02-08). "Memory Foam Mattresses: Benefits and Disadvantages". WebMD.
- ^ a b Laurie Brenner. "Memory Foam Dangers". SFGATE (website of the San Francisco Chronicle). Retrieved 13 May 2019.
- ^ "Is Memory-Foam Bedding a Fire Risk?". 11 September 2011. Archived from the original on 2015-07-26. Retrieved 2015-09-09.
- ^ "Federal Mattress Standard - Bureau of Home Furnishing and Thermal Insulation". ca.gov. Archived from the original on 2008-09-16.
- ^ Arlene Blum The Fire Retardant Dilemma Archived 2009-06-05 at the Wayback Machine. Science. 12 Oct 2007: 194b-195b.
- ^ Federal Register / Vol. 61, No. 250 / Friday, December 27, 1996 / Proposed Rule: Environmental Protection Agency Archived January 9, 2012, at the Wayback Machine and Environmental Protection Agency Archived 2012-01-09 at the Wayback Machine Federal Register / Vol. 63, No. 194 /Wednesday, October 7, 1998 /Rules and Regulations
- ^ Environmental Protection Agency Archived 2012-01-09 at the Wayback Machine Federal Register / Vol. 63, No. 194 /Wednesday, October 7, 1998 /Rules and Regulations