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How memory foam reacts to heat

Memory foam is polyurethane with additional chemicals increasing its viscosity and density. It is often referred to as visco-elastic polyurethane foam. In some formulations, it is firmer when cooler. Higher density memory foam reacts to body heat, allowing it to mold to a warm human body in a few minutes. A lower density memory foam is pressure-sensitive and moulds quickly to the shape of the body.

Contents

History

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. Yost named the temperature-sensitive memory foam "temper foam".[1]

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 bony regions decreased or stopped the blood flow to the region causing pressure sores or gangrene. Memory foam mattresses remarkably decreased such events.[1]

Memory foam was initially too expensive for widespread use,[citation needed] but in recent years it has become cheaper. Its most common domestic uses are mattresses, pillows, and mattress toppers. 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.[citation needed]

Properties

A memory foam mattress is usually denser than other foam mattresses. 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 solidness of a firm one. Memory foam mattresses often sell for more 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 an accurate measure on "soft" and "firm". A higher IFD foam, with a 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 12). Most memory foam mattresses are firm (IFD 12 to IFD 16).

Some 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.[2] 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.

Memory foam has an open cell structure that reacts to body heat and weight by 'moulding' to your 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 means different mattresses feel very different. A high density mattress will have better compression ratings over the life of the bedding. The lower density will suffer from slightly shorter life due to the compression that takes place after repeated use.

Cell structures vary from very open, to almost close cell. The tigher the cell structure, the less airflow through the foam. Memory foam has been known to be very hot to sleep for some. "Breathable" visco-elastic foam will have a more open cell structure, allowing higher airflow, better recovery, and lower odor retention at packaging. The cell structure has little to do with the slower or faster recovery.

Very high levels such as 5.3 lb/ft3 (85 kg/m3) are used infrequently in mattresses. Tempurpedic have been known to make them.

The amount of memory foam also has an effect on the capabilities of the mattress or topper. Anything less than 2 inches will not have much of an effect, whereas a 6 inch block would be too soft and dense to sleep on comfortably.

Each mattress, therefore, is a combination of its height, density, and type, each of which will have different properties.

Hazards

When new, some memory foams give off a distinct chemical odor, which many people find unpleasant and some say is akin to the smell of paint. This odor decreases with airing, but some remain sensitive. Emissions from memory foam mattresses may cause more respiratory irritation than other mattresses. Mildew and house dust mites may not occur as frequently so asthma attacks may be less frequent and severe. [3]

Memory foam, like other polyurethane products, can be combustible.[4] 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. New bedding laws that went into effect in 2010, change the Cal-117 Bulletin for FR testing.[5] There is concern that high levels of the fire retardant PBDE, commonly used in memory foam, could cause health problems for users. [6] PBDE's are no longer used in most bedding foams, especially in the European Union.

Manufacturers caution about leaving babies and small children unattended on a memory foam mattress as they may find it more difficult to turn and rotate and may suffocate.

References

  1. ^ a b NASA spinoff database
  2. ^ Polyurethane Foam Association - Density Standards and Guidelines
  3. ^ Anderson RC, Anderson JH, Respiratory toxicity of mattress emissions in mice, Archives of Environmental Health, Jan-Feb 2000
  4. ^ Memory Foam MSDS Sheet
  5. ^ California Bureau of Home Furnishings and Thermal Insulation
  6. ^ Arlene Blum The Fire Retardant Dilemma. Science. 12 Oct 2007: 194b-195b.
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