Memory foam is made from polyurethane with additional chemicals that increase its viscosity level, thereby increasing its density. A polyurethane, commonly abbreviated PU, is any Polymer consisting of a chain of organic units joined by urethane links Viscosity is a measure of the resistance of a Fluid which is being deformed by either Shear stress or Extensional stress. The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different It is often referred to as visco-elastic polyurethane foam. Viscoelasticity is the property of materials that exhibit both viscous and elastic characteristics when undergoing deformation. A polyurethane, commonly abbreviated PU, is any Polymer consisting of a chain of organic units joined by urethane links The most general definition of foam is a substance that is formed by trapping many gas Bubbles in a Liquid or Solid. Depending on the chemicals used and its overall density, it is firmer in cool temperatures and softer when warm. Higher density memory foam reacts to body heat which allows it to mould itself to the shape of a warm body within a few minutes. A lower density memory foam is pressure-sensitive and will mould more quickly to the shape of the body. The example often used to demonstrate its properties is that a hand pressed into the foam and then removed will leave a clear impression in the foam.
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History
Memory foam was originally developed by NASA to decrease the very high pressure caused by the extreme g-force occurring during the take-off of the space shuttle. The National Aeronautics and Space Administration ( NASA, ˈnæsə is an agency of the United States government, responsible for the nation's public space program g-force (also G-force, g-load) is a measurement of an object's Acceleration expressed in g s It was never used in the space program but was subsequently used medically, for example by patients who used to lie in bed on hard or very firm mattresses for long periods of time without regularly moving such as being bed-bound after a paralyzing stroke. The pressure over some of their bony regions decreased or stopped the blood flow to the region causing horrific pressure sores and/or gangrene. Bedsores, more properly known as pressure ulcers or decubitus ulcers, are Lesions caused by many factors such as unrelieved Pressure; friction Please do not add warnings to this page about the pictures Wikipedia is not censored for taste and has a guideline preventing such warnings - WikipediaNo disclaimers in articles Memory foam mattresses helped hugely to decrease such events.
Memory foam was initially too expensive for general use, but in recent years it has become cheaper to produce and is now widely available. Its most common domestic uses are mattresses, pillows and mattress toppers (also known as mattress pads). A mattress is a mat or pad usually placed atop a Bed, upon which to sleep or lie A pillow is a large Cushion support for the head, usually used while Sleeping in a Bed, or for the body as used on a Couch or Mattress toppers are designed to lie atop an existing Mattress. It still 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.
A memory foam mattress is usually denser than an ordinary foam mattress. This makes it more supportive – but also heavier. It is often seen as a good compromise between the comfort of a soft mattress and the supportiveness of a firm one. Memory foam mattresses often sell for more money than traditional mattresses but they last longer.
The property of firmness (hard to soft) of memory foam is used in determining comfort. Firmness is measured by a foam's IFD (Indentation Force Deflection) rating.
IFD measures the force (in pounds) required to make a dent of 1" into a foam sample 15" x 15" x 4" by a 8 inch diameter (50 sq in) disc - known as IFD @ 25% compression. This article deals with the unit of force For the unit of mass see Pound (mass. 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).
Hazards
When new, some memory foams give off a distinct chemical odor which many people find unpleasant which some say is akin to the smell of paint. This odor decreases with airing, but some people remain sensitive to it. Emissions from memory foam mattresses may cause respiratory irritation more than other mattresses. Mildew and house dust mites may not occur so frequently so asthma attacks may be less frequent and severe [1]
Memory foam, like other polyurethane products, can be combustible. A polyurethane, commonly abbreviated PU, is any Polymer consisting of a chain of organic units joined by urethane links [2] State and US Federal Laws have been enacted in the USA to require all bedding, including memory foam items, be resistant to ignition from an open flame such as a candle or cigarette lighter. [3] There has been some concern that high levels of the fire retardant PBDE, commonly used in memory foam, could cause health problems for users of memory foam bedding products. Polybrominated diphenyl ethers or PBDE, are Organic compounds that are used as a Flame retardant.
References
- ^ Anderson RC, Anderson JH, Respiratory toxicity of mattress emissions in mice, Archives of Environmental Health, Jan-Feb 2000
- ^ Memory Memory Foam MSDS Sheet
- ^ California Bureau of Home Furnishings and Thermal Insulation
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